Äh...Spot the paradoxon, or where is the chicken and where is the egg in that narrative?
Can the poor performance of the RKKA throughout the war be truly attributed to a failure to implement its doctrine properly, or was not rather its doctrine ill suited, arguably even the root cause of its troubles?
Mind you, even when fighting against a depleted, numerically and materially outmatched, even essentially premodern opponent like the mid-late war Wehrmacht, the Soviets kept incurring disastrous casualties and no shortage of operational setbacks which they would have never been able to afford agaisnt a peer opponent. Similar to how they fared against the Finns in 1940 come to think of it.
I don't think the Soviets can be entirely absolved on the doctrinal front given that they had essentially 7 years of interrupted, high-intensity combat (Nomon-han to VE day, or August Storm if you will) to smoothen out questions of "application".
What do you mean by disastrous soviet casaulties in the later years of the war? As far as i'm aware during 44-45 the casaulties of the soviets did not exceed the casaulties of the wehrmacht, And in 1943 the casaulties were not really "disastrous" either. Even if the soviets did suffer higher casaulties, they were able to sustain them much better than the wehrmacht.
The most reliable data is 8.7 millitary deaths of the soviets vs 5.2 million deaths of all axis forces on the eastern front. Hardly disastrous, IMO.
The casaulties in 1941-42 were of course horrible, but so were the casaulties for the wehrmacht in 45.
And even with all the shortcomings of soviet doctrine, i dont think its fair at all to call it disastrous... Especially compared to the performance of allied armies in 1940 during the invasion of france, or the performace of the british in the south eastern theatre.