Maxims + AT rifle cons + ML20 is a very potent combo in teamgames. Whether it's too strong I can't say but it might be quite dominant on narrower maps.
Example:
https://www.coh2.org/replay/66206/2v2-dbp-v1-6-1-usf-sov-vs-ost-okw
Luftwaffe doesn't seem to offer very much, perhaps a more radical revamp?
RE. Flame hetzer
Cost and CP increase would be helpful here. More concerned about its retreat wiping strength, which is considerable.
usf mortar HT
Strength isn't so much synergistic as opposed to its pinpoint accuracy and ability to strip squad HP (from full health squads) and wipe weakened squads very reliably. results in having to play extremely cautiously with squads (can't cap even after winning fights, squads go into combat and have to retreat very quickly for fear or instant death, etc). Not enjoyable gameplay
76mm Sherman
increasing HP would make it overlap with the ez8 and dozer upgraded sherman even more. If its meant to be a mobile tank hunter that you amass and throw in to trade for axis armor perhaps something more unique would fit this role.
Minedrop
S-mine like ability would be good (though potentially even stronger bc retreat wipes). maybe lower lethality slightly to compensate
Greyhound
4CP is a good starting point.