The m10 has faster speed, a turret, a bit more health, 0.75 moving acc and I believe HVAP too. Way better than a Stug.
The M10 has faster speed and a moveable turret, thats right, but this was about surviability which dind't get boosted by that.
Although you may think it can be a flanking tank because of its speed you will be quickly convinced to use it otherwise if you try. Range 50 and too slow rotating turret define its role at the same spot as Stug G. In most cases you will stop it to shoot, so the 0.75 moving accuracy isn't that great deal for a ranged TD, its way better for flanking tanks or infantry support tanks like the Sherman.
So M10 and Stug G will engage enemy tanks frontally in most cases. M10 has same health as Stug (its the Stug J that has slightly less health) higher size (22 to now 17) less armor and less penetration (at Vet 1 you can pay ressources for HVAP to get more penetration) but a slightly higher ROF. All together: In spite of beeing doctrinal and beeing bind to USF T4 tech M10 will loose this fight versus nondoctrinal T3 Stug.
For USF this doesn't even matter because there is no reason to take a M10 over a Jackson which is in the same tech and can do its job better from a greater range, especially if M10 looses to Stug (so the M10 is in a far worse spot than Stug was). But it could be important for USF, because there this tank could be useful actually it it gets a little bit of care.