I seem to recall that when the jerries invaded Russia in ‘41 that the Russians did quite poorly so Stalin replaced the head military guy with Zukhov and then tide changed for them. Hopefully nothing like this happens in the UKR.
Plus a major difference is that in ‘41 the Russians were defending their homeland. Not the case this time.
a lot of the initial massive losses were because of stalin's own decisions - his refusal to see the incoming invasion meant the air force was destroyed on the ground, his refusal to allow retreats meant massive encirclement and surrenders. yes, a lot of the generals thought the same way, ordering disastrous frontal assaults, etc. but that is more culpability for stalin - he had massacred most red army officers in his purges, so these officers were in their posts because of his actions. not sure there's anything comparable here.
and of course the difference here is also, as you said, a defensive war where the losing outcome was annihilation, versus a "special military operation" against a hostile population.
finally, based on some of the videos and tweets here, the problem with the russian army seems to be at every level, from common soldiers deserting to incompetent officers to out-of-favour generals. not sure a single change at the top can fix all that (and tbf, it took a lot more than zhukov for the tide to change in ww2 too)
I think the tide changed with the Lend-and-lease act. The soviets were pretty much done concerning decisive war materials / resources.
lend-lease helped massively with trucks and also with food, but the vast majority of tanks, planes, rockets, guns, were all made in the ussr.
a big reason the ussr lasted was because they managed to relocate their factories behind the mountains at insane speed, dismantling entire factories, putting them on trains, and rebuilding them quickly. otherwise they were easy fodder for german bombers and advancing armies.