I think the HM-38 is fine, especially after the nerf to its auto-attack range with the most recent patch. This 25% bonus range was one of the major advantage it had over other indirect options as it not only meant that you could park the mortar in relative safety to fire away with minimal user input, but also that it outranged most of its indirect counters. Now that this is gone the HM-38 still deals a bit more DPS/area than its counterparts thanks to the good AoE-to-scatter ratio, but this is also counteracted by the significantly lower ROF.
The only area where it truly shines is the barrage, which is much more useful now with the reload speed buff it got recently. Using the barrage, however, means you need to actively manage where you want to shoot and when, so the extra range and DPS are much more justified than they were for the auto-attack.
As for the odd 1-man survivability perk, AFAIK this is somewhat hard-coded into the game and can't really be changed. Hence why the crew size has already been decreased to 5 men from the standard 6 for other soviet team weapons a long time ago. I don't think further nerfs to this would really be necessary.
What?
le.IG 18
1) Squad strength 4
2) Minimal crew 2
3) Lack of retreat opportunities
4) weak AOE
5) the range is the same as that of the HM-38
6) 7.5cm Incendiary Barrage is only in one doctrine!
Is this supposedly OK? Unkillable Soviet units - "this is OK, cannot be fixed, nerf is not needed", German Squad strength 4 with Minimal crew 2 - "this is balanced." UNDERSTAND.