Penetrating shot nerf
Penetrating shot got 1.000 penetration which is a huge buff to its AT role and price reduction from 70 to 60 and now fire the projectile faster.
As for AOE its Kill radius might have gone down but its FAR AOE was increased 1.5 and the far damage was tripled.
I doubt this qualifies a straight nerf.
M3A1:
HP n armor nerf
HP went up not down. Overall it about 10% EHP reduction and bringing armor value close to other vehicles.
Late game nerf (you end up paying for something you were getting for free) and the expense of getting it faster at T3 timing if you pay for it.
...
Remember that Grens get this for free at T4 and this didn't solve all the complains with Grenadiers in the late game.
MR can become available from around minute 6 and the XP gain kick in for both units immediately and the reinforcement reduction for Penal.
As an investment it can return value for much longer time than "all out war".
Imo you are underestimating the time factor.
Finally one has to keep in mind that Ostheer received minor buff and mostly nerfs especially in their crutch commanders and OKW where not doing that great to being with.