Is there no way to use old Field Marshal only army group? As i find the new system does not work well with large fronts, like russia where i am trying to squeeze in 300 divisions, 15 separate Generals under 3 FM is crazy to control and they dont seam to be effective pushing forward or at covering the whole front line (they keep leaving gaps for the enemy to move in)
I don't actually understand this. This point is sometimes raised, but I still don't.
I was playing China. In the end I had 624 divisions (yeah, not so many, but I stayed on limited conscription because roleplay, immersion and economy). Some of them were united in Army Groups for 72+ divisions, each under Field Marshal and with separate generals on every army. Until I fought against minors I just gave this army united order. I didn't tried to control separate generals as separate generals - I make full order for Army Group, with exception of mine tank storm groups (who got separate orders about blitzing).
That actually went nice for me on four-front (India, Middle East, Siberia, Turkestan) fight against Soviets with a lot of breakthroughs. I started to do it manual in the end of war, when I just run my mobile divisions without any plans or covering flanks for the VPs (it was run against USA), and even then AI generally did good work in closing holes I created.
Does it mean we have to deal with a poor garrison order (plan so ?) if we want to put more than 24 div under a general commander because we can't do that with a field marshal anymore ?
No. You can make one garrison order for full army group (and it can be without actual FM), that gives you 72*5=360 divisions on same order (I actually stayed in 120, with every army being 24, because I thought I could actually use them if things go south; things never did). One such order allowed me to cover full Japan at once.