Caveats - playing Ger exclusively atm. up to lvl 6 campaign.
Some ideas, some complaints, suggestions, and questions, so bear with me 
ive played a lot of betas over the years, and historical games, and consider myself to be “average” - but balance shouldnt just be based on top 2% of players imho
1- weapons are good, feel about right, nice mixture.
2- grenades also fine.
3- mines? AT mines? possibly ? engineers ? (though id avoid infantry mines for spamming reasons)
4- love the skill-perk system for soldiers
5- squad building with various types is spot on aswell
6- unlocking classes - is there an advantage to a longer served person who can have bigger AND better squads ? will that lead to seal clubbing complaints ? new person vs veteran could be… messy.
7- LOVE the squad ai mates - its the whole shtick . and what drew me in in the first place - i dont really see the point of solo “lone fighters” mode though ? leave battlefield to battlefield imho - dont try to be all things to all people.
8- Engineers - AA guns have bugger all ammo - i get you dont want them spamming vs infantry - possible solution make the ‘gun build’ be a flak pit, not just a gun, so it can only fire up ? and give it more than 5 magazines (again only used the Ger one )
9- Engineers2 - if you have 2+ engis in squad, and they arent being shot at - make them assist with building ? 20% time reduction per additional person, or such ?
10- mortars , flamerthrowers - not used them yet, but have been on receiving end, dont feel they are OP - this may be due to noob use, but certainly were more interesting than map-winning.
99- the planes. URGH. Ger = 1936 dive bomber, (with no rear gunner ?! ) [4] and a crappy fighter [7] and monoplane [15] Vs a 1941 cannon ground attacker [4]? really ? - i hope that its a placeholder as it was done first rather than an indication of the balance of vehicles going forward [anyone ever heard about the “russian bias” in War Thunder ? …]
sure ill think of more in due course 