There are a lot of people who think their own approach of playing the game is the only right way. Take what people say with a grain of salt. People have specific playstyles and they will give what goes best for that playstyle, and they will assume their advice will work for everyone else. Best you can do is to try out stuff on your to your own liking.
Even people are writing stuff like "CAS is best even in large USSR". This is in 90% of all circumstances just WRONG.
Read all the tooltips and go with what you like the best and make it work.
To some extent, it's useful to realize that most of this advice actually works in SP if you micromanage effectively, because the AI doesn't. 20:1 with 10 infantry battalions and support is attainable with nothing else in terms of divisions, and easy if you have air superiority. Nobody should pretend such a setup is optimal/ideal in most cases.
Rather than worrying about 10 vs 20 vs 40 as USSR, a foundation of knowledge in the game should let players win with any or all of the 3 in SP. Once more experienced, it's important to understand what outperforms alternatives in each scenario and why. That reasoning is how you actually counter stuff, should you ever need to do so.
Aeon gives sound advice for example, but getting width screwed by tactics --> shoved back means a lot more on some fronts than others. If your line breaking cause you to die, this is a dominant consideration. If you're more concerned about equipment or manpower efficiency and are in a strong position maybe you just go 40 width anyway. He even gave reasoning why a tank width would therefore be better suited at 40w, but not all infantry if you infer the rationale properly.
A rookie player needs to be processing the "why" of the advice, because understanding that is the way to improve. That, and practice micro because in SP you can seriously win with almost anything halfway competent, and if you do fight good players later they'll have the compositions AND the micro.