Have you tried the M1919? It's incredibly strong. So are assault engineers and the bulldozer sherman. AT guns from airborne let you skip captain. Dunno if I'd say the options are weak.
That's offtopic though... I do think it'd be smart if they let people buy the commanders just 'cause they could make some money that way and I don't really care if people can pay to get them.
I have tried to make use of all three.
Airborne: M2HB costs 20 mp less than non-doc MG and comes with 0 men. AT gun costs the same and also comes with 0 men. Pathfinder is more of a utility unit, in 1v1 I cant afford utilities. AB looks good on paper, but it needs pathfinder to reinforce and M1 carbines are peashooters, the worst part is that they carry no AT. Obersoldaten carries no AT and its fine because everyone and their dog in OKW can do AT, not to mention Obers are twice as good as Airborne at AI, and cost less. 240 muni strafe, Ha!
Armor: Assault Engineers costs the same as rifles and has no range and no AT, maybe I can get away with this in team games. M10 is a Tank destroyer that has only 40 range I believe, because when I did shoot ground it only shoots as far as a sherman. Sherman bulldozer has no penetration, it's like a kv8 except it does half as much damage to infantry and has less armor and health, and kv8 is already useless. And we are left with railway artillery and crew with Thompson. I hope somebody tries to use crew Thompson sometimes, I do like free vehicles.
Infantry: The only useful ability in this tree in a 1v1 situation is the M1916 unlock, it does virtually identical damage as the Ostheer Grenadier's LMG42 and even costs the same.
I don't have the premium ones yet nor have I played against any. But flamethrower riflemen sounds very strong, and free exp for new rifles at cp 0 is probably borderline OP. The WC51 car I don't know since I wasn't in alpha, but I have seen it described as M3 from hell. Well I do like my M3s
