If the Soviets excelled in their military equipment, why were the Germans able to inflict such heavy casualties on them through-out the war?
Having good equipment doesn't mean you're using it effectively. And the side that wins is not necessarily the side that takes the least casualties.
First, how could they take so many casualties with superior equipment?
When the Germans invaded the Soviet Union they had a lot going for them. Surprise, superior tactics, good communication, and independently thinking officers. The Soviets had none of that. What they had was numbers, some superior equipment, and room to retreat. But it wasn't always that way, and it wouldn't last after the first year of the war.
Between WWI and WWII, the Soviets were on the cutting edge of military technology and thought. Germans and Soviets, both pariah states, worked together on developing new military equipment and tactics. What we know as Blitzkrieg was conceived by the Soviets as Глубокая операция aka Deep Operation. They'd invested early in tanks and aircraft, new technology at the time, and concentrated them into Mechanized Corps for rapid, deep thrusts behind enemy lines.
Then in the late 1930s came the Great Purge. Much of the Soviet military leadership was executed or exiled. What was left were mediocre party hacks, incapable and unwilling to do anything but follow orders to the letter. Division commanders had to answer to political officers. Deep Operation, being the idea of purged officers, was discredited. Their tanks were dispersed to support the more ideologically acceptable infantry.
The disaster of the Winter War of 1939/40 humiliated the Soviets and made their military the laughing stock of the world. As a result some reforms were begun. Commanders were called back from exile. New units were formed. But it wasn't enough and they were out of time. They thought they'd bought themselves more time with the Molotov-Ribbentrop Pact of non-aggression, but the Germans did not honor it.
Although the Soviets were able to mobilize, Operation Barbarossa was a surprise attack. By concentrating their forces the Germans achieved numerical superiority in manpower over the Soviets in the opening attack. WWII was fought at a pace never before seen and only the Germans had the experience and training to fight it. They had by this point successfully invaded Poland, Norway, France, and the Balkans all with a speed and ferocity no one else could yet match.
Just as the Allies could not keep up with the Germans in the Battle Of France, the Soviets could not match the pace of the German attack. It could take hours for information to work its way up command, for the commanders to make their decisions, and for new orders to work their way back down. By that time the situation would have changed and the orders would be woefully out of date. The Soviets, like everyone else, could not keep up with the pace of Blitzkrieg. As a result their armies were encircled and wiped out. Hundreds of thousands of troops were captured in the opening weeks.
On a tactical level, the Soviet army was very poorly trained. Soldiers who had never seen a car before might be driving a tank after a few hours training. The lack of training meant infantry could mostly manage frontal wave attacks instead of outflanking or advancing with fire and movement.
It was a great German innovation to give every tank a radio (keep in mind in 1941 radios were bulky and expensive and unreliable) allowing coordinated maneuvers even in the heat of battle. Most Allied tanks of the period had no radio and communicated with flags allowing only the simplest of tactics and almost no control during battle.
The T-34 and KV-1 were equal or superior in the important areas (firepower, protection, mobility) over any German tank of 1941, but they were relatively few (only a few thousand). Individual actions lead to heroic stories and often threw off tight German timetables, they were more often very poorly used. The vast majority of the 23,000 Soviet tanks were outdated light tanks such as the BT-7 and T-26. While a qualitative match for the still numerous German Panzer II, their poor tactics meant they were cut to ribbons.
Fortunately for the Soviets (and everyone) a combination of German overconfidence, stubborn resistance by the Soviets, and Hitler's amateurish meddling diffused the German armies' striking power. They fell just short of Moscow before winter set in. Long supply lines, a dilapidated transportation system, a lack of logistical preparation for a long war, and surprising continued Soviet resistance further hampered the Germans
As the war drew on the Soviets recovered from their initial shock. The outdated equipment had been destroyed. New equipment equal to the Germans was pouring off the production lines. More men and equipment were being shifted east. The Moscow and Leningrad were holding. Most importantly, they were learning from the Germans how to fight. In late 1942 this all culminated at Stalingrad when the overstretched Germans were halted and surrounded in an enormous envelopment called Operation Uranus that clawed the guts out of the German army.
Why did the Soviets take so many more casualties than the Germans? To put it simply: because they could and the Germans couldn't and that was how they were going to win the war. It was a cold calculus that the Soviets could not match the Germans in tactics and training, but they could replace men and machines faster than the Germans could and they were going to use that to win.
In 1941 that was not nearly enough. Soviet tactics and training were just too inferior, and there were too few of their modern equipment. Even then the sheer size of the Soviet army and scale of the Soviet Union slowed the Germans enough to survive, plus some stubborn resistance. With Soviet tactics and equipment always improving by late 1942 they had sufficiently closed the gap with the Germans to overmatch them.
While at the Battle Of Kursk the Soviets lost tanks and guns at a rate of 3-to-1, but because they held the field they could recover and repair their vehicles while the German loses were gone forever. Through repairs and manufacturing the Soviets were back up to strength in a month, but for the Germans this was their final throw of the dice on the Eastern Front. The Germans could not replace the lost equipment fast enough to concentrate enough firepower for an offensive campaign on the scale needed on the Eastern Front and hold off the Allies in Italy and guard against an expected invasion somewhere between Southern France and Norway. The Soviets knew it. From now on the Germans would be fighting on the defensive.
Note: the casualties of the Battle Of Kursk are often mixed in with the follow up Soviet counter-offensives Operation Polkovodets Rumyantsev and Operation Kutuzov wherein the Soviets took very heavy casualties, particularly in armor.
There is a simple reality of war that you fight with the army you have. The Soviets did just that. They had a very large but under-trained army. They had a range of equipment from some of the best to some of the worst. All of which could be replaced. They had poor communication and coordination, but lots of room to fall back. They eventually learned how to avoid being surrounded by the Germans and how to use their superior numbers and effective equipment to concentrate force and land hammer blows of their own, blows from which they knew the Germans could not recover.
- The Soviet Union purged their military leadership prior to the war and crippled it with the commissar system. When they finally allowed the military professionals to fight, they became much more effective.
- German weaponry was superior in a few specific aspects. Many of their tanks had worse guns and better radios, while Soviet tank platoon commanders had to use signal flags.
- At the beginning of the war, Germany achieved surprise and inflicted massive casualties.
It took the Soviets some time to regain their balance. Then they won.