Srsly tho some interesting questions here. Maybe I can add some food for thought
I’m pretty sure Malanichev also does ab work fwiw
Also worth noting that this is a training style that works well for Malanichev obviously but among the top competitors in the world you see many different training approaches. He doesn’t recommend it for everybody else nor does he claim it is in anyone the best approach for others. Hell it could just come down to preference. Still there’s always something to be learnt.
Anyways often it’s the training that got someone to the top that we can learn more from and take from than an elite level lifters current training style.
Define work. Volume x Intensity? In physics work done is defined as product of the force and the distance over which the force is applied. In the end work is the stimulus then you recover and hopefully end up adapting and making gains. When you are squatting Malanichev’s kind of working weight for reps it’s literally a lot of work.
At Malanichev’s level he is moving so much weight that he gets a lot of work/fatigue generated just from a few working sets. After all this work he also needs to recover. A dude squatting 405 for reps can do it thrice a week no problem but with 7,8,900 lbs I don’t think anything human being with all the drugs in the world could manage to recover from that.
So I would say for Malanichev a low volume low frequency approach makes sense.
On frequency we need to have a think about why many lifters go high frequency. Technique practice (Malanichev’s form is engrained and automated by decades of practice), squeezing in more work in the same time frame (again he does plenty of work already), etc.
On assistance exercises: why do we do them? Improve weaknesses e.g. long pause bench or pause squat (Malanichev doesn’t have a glaring technical weakness which really needs addressing), get in more work e.g. close grip bench or high bar squat (Malanichev already gets in plenty of work and anything near max effort will add on loads of fatigue). I don’t know your source of info but I’m pretty sure Malanichev sparingly includes variations/assistance movements in the off season.
Lastly on muscle imbalances you may kinda have a point here. Between deadlifts, squats and abs I think everything from the nipples down is more or less good to go. Maybe benching isn’t balanced out by setting up your shoulders for bench, pulling heavy from the ground, and creating a tight back for squatting. Still the man himself cares more about lifting world record totals than building a balanced healthy physique. If asked about injuries he’d probably tell you “too many” in Russian.