It might the slight nerf that the Jackson could take without interfering with the rest of the balance.
Decent idea. 5-10 armor nerf might actually be enough so that a P4 would hit very reliably. The only thing to watch out for is indeed the Puma since it could be a very easy and sacrifice to get a Jackson that might have already been hit. Especially with the smoke it could really cheese a Jackson kill if it penetrates too reliably.
Is the Puma being a counter to the Jackson that bad an idea though?
The Jackson is the only tank destroyer in a faction who's AT is otherwise all geared towards killing lights (low pen ATG, low pen bazookas, pathetic pen Stuart).
If the Jackson needs a vehicular counter, what better vehicle than the one USF is best equipped to deal with without a Jackson?