The puma is also useless against infantry, whereas the Stuart is at least decent. That's the trouble with the Stuart, and to some degree the AEC: they're not quite AI-focused like the Luchs, T70 or 222, but they're also not quite AT focused like the Puma.
Compared to other AT-LVs, the Stuart also has a vehicle crew, which is a considerable bonus that (imo) offsets the lack of smoke.
Would you ever build the Stuart if building the AEC or Puma instead was an option?
The current Stuart sacrifices the Puma and AEC's scaling for mediocre AI USF doesn't need and excessive armour that's only good for messing up the Ostheer matchup.
This would simply make it less worse than the Ostwind. Key being that it would still be worse than the Ostwind. Any buffs combined with price increases will just bring it further in line with the Ostwind or Brummbar, making it redundant.
Another option could be to nerf it and reduce its cost so that it comes at around the same time as the OKW puma so that the light tank gap in Ost's roster would finally be filled. this was suggested by Unit G17 in the Ostheer tech restructure post.
My suggested tech rework would accelerate its timing a fair bit.