Firstly; nice video. It covers all the points well, and is just well made. Great work.
Changes As Follows
-Barrage recharge from 80 to 30
-Speed from 6.3 to 6.7-6.9
-Rotation rate from 32 to 36-38
Secondly;
no to all. This will brick OST and turn the STUG-G, which is already pretty underwhelming, into an absolute joke. Let's compare the current stug to the proposed 'buffed' SU-76.
SU-76
280mp, 75f, 8 pop
400mp, 75/35 armor, 20 size
6.8 or 6.9 speed, 2.3/4.4 acc/deacc, 36 or 38 rotation
120dmg, 160 far pen, 4.9-5.4 reload, 60 range
STUG-G
280mp, 90f, 10 pop
560hp, 140/70 armor, 17 size
6 speed, 2.1 accel, 28 rotation
160dmg, 170 far pen, 4.5-5.5 reload, 50 range
So; for 15 less fuel and 2 less pop, you get a unit that would be
untouchable by the more expensive STUG; it would accelerate much faster, has a much higher top speed, and turns faster, while also having 10 more range and a 100% chance to pen it at max range.
That would be 'fine', but it also pushes the speed above every other OST unit. P4 dives? The P4's top speed is 6.3 with 2.1 acceleration; it also wouldn't be able to actually catch it. Even the panther's 6.6 speed and 2.4 acceleration wouldn't be able to catch it. Meanwhile, the SU-76 would have 10 to 15 more range than either of those units.
Realistically, OST's only counter would be the doc-locked Puma (7.2 speed, 4.5 acell), but its main benefit is being able to flank. With the SU-76s buffed rotation speed, it would need to circle-strafe the Su-76 at a very close range, making it extremely vulnerable to snares (since its also insta-snared).
Now, you might say that this is OK, since it would still be very squishy. That would be fine, but you're also pushing it more into the "support artillery" role. At 80 range, the SU-76 out-ranges any and all AT OST has to offer, except the Elefant. But now its going to be barraging every 30 seconds (in teamgames, you'd have the res) - which would be incredibly powerful against the
largely static OST units (MG42, Pak40, LMG Grens, etc.).
Additionally, it'll be doing those constant barrages while being immune to counter-barrages. In your video, you brought up that the Zis-3's cooldown is 30sec vs. 80 on the SU-76; the reason for this because the Zis-3 is vulnerable to counter arty. While it can fire more often, it can be quickly decrewed; a barraging SU-76 isn't at risk from mortars, LeFHs or even PWerfers.
So, essentially, you're suggesting making the SU-76 an early-game TD that's faster than
every stock AT solution OST has, while also being incredibly cheap. Then rounding out its late-game squishy nature by giving it an incredible secondary role.