This will focus on more historical accuracy and better balance.
Firstly BA changes from Stalingrad need to be imported!
Axis:
The starting gear is the same.
Level 2: Assaulter I - MP34
Level 3: Engineer I - VZ24 (the same)
Level 4: Figter pilot I - Hs 123 - A-1 (the same)
Level 5: Sd. Kfz. 231 (8-rad) (Light, fast, decent gun against early tanks) + MP38 (the same)
Level 6: Radio operator I - Mannlicher M1895
Level 7: Attacker pilot - JU-87 B2 (The same)
Level 8: Pz 38(t) Aufs. S (This is one of the main vehicles of the german blitzkrieg and early war, how isnt this in the tech tree is confusing to me) (This is slightly different than the premium)
Level 9: AT gunner I - PZb-39 (Pzb 38 replaced, theyre basically the same, just recycle a late level) + AT Gebalgeladung grenade bundle (Can disable or even knock out tanks with a well placed throw)
Level 10: Machine gunner I MG13 (The same)
Level 11: MP40 - (the same)
Level 12: PZIIIJ - (its 50mm armor cannot stop 45mm shells, turret traverse is the super slow, doesnt deserve level 29 unlock)
Level 13: ZB26 (the same)
Level 14: Mortarman (The same)
Level 15: BF109 f1 (1x 250Kg bomb instead of 4x 50kg)
Level 16: Steyr Model 1895 (sniper)
Level 17: Trooper II K98k w/grenade launcher (The same)
Level 18: Flametrooper I - FmW35 (The same)
Level 19: Bf110 C-7 (The same)
Level 20: Machine gunner II - MG34 (The same)
Level 21 Engineer II - G41 (The same)
Level 22:Tanker II: Stug III A (With HEAT)
Level 23: MP35/I
Level 24: Sniper II - Gewehr 98 (Sniper) (The same)
Level 25: Attacker pilot II - Dornier Do 17 (4x 250kg)
Level 26: Assaulter II - BerettaM38 (40 rnds)
Level 27: Selbstladegewehr 258(r) (Captured SVT38) - (This is historically accurate, germans loved the SVTs, since the G41 was trash and used them quite a bit)
Level 28: AT gunner II - GRb 39 (The same)
Level 29: PZIIIJ/I (Fair fight against the T50, and can hold its own against a T34, but isnt even close to an equal)
Level 30: Assaulter III: Maschinenpistole 716(r) (Captured PPD 34/38)
Level 31: Sniper III - ZH29 (Sniper) or G41 (sniper) (or even a captured SVT sniper but not a fan of that one)
Level 32: BF109 E-4
Level 33: Flametrooper II - FmW41 (The same)
Level 34: Tanker III - PZIVF1 (the same)
Level 35: Kiraly 39M ( The same)
Level 36: Attacker pilot III: Ju87 r-2 (1x 1000kg bomb)
Level 37: PZIIIL (More than a match for the T34, and mostly immune from the front against the most common soviet AT gun - 45mm)
Level 38: Trooper III: K98k w/AT grenade laucher ( ) + Sdkfz251 (1x MG34) (This squad would spawn with the vehicle)
Level 39: Assaulter IV (Suomi KP31)
Level 40: Gunner III: MG34 With paramotel (75rnds)
Level 41: Tanker IV: 8.8 cm Flak 18 Sfl
Allies:
I will list what is different only.
Level 15: Yak1 (2x 100kg (forged) bombs)
Level 22: BT-7A (F-32) 76mm gun, and an extra MG on the roof, light and fast.
Level 23: PPD40
Level 26: Captured MP40
Level 30: Assaulter III - Thompson 1928 (box)
Level 31: Sniper III - PTRS1941 (Sniper) (effective only while prone or mounted)
Level 35: PPSH41
Level 37: T34 (1940) (the same)
Level 38: Trooper III: M91/30 w/AT grenade launcher + IZ improvised armored truck. 45mm cannon and a DT 7.62 MG.
Level 39: 1928 thompson (50 round drum)
Level 40: Gunner III: DT29
Level 41: KV1 (L11)
That is my opinion, and i think it would be A more historical, and B better balanced