Mobile defense archieves little against anyone with half a brain, as they will just get an Su-76 or a Zis afterwards (or both).
In general I really don't get the people who say OH of all factions is strong this patch....its just not.
Thats the point, SU-76's don't really do well against Puma's. You can use smoke to cover your assaults and for when your retreating. Puma's use the old TWP that guarantees penetration and you can easily stun lock tanks with two.
Like it's not about strait up beating your opponent in every battle it's about bleeding him down to nothing till he just can't bang his head against the wall anymore. Check my replays if you want any examples. (My latest one even got casted!)
The CPIV is also insanely durable in mobile defense because you get smoke + the .8 damage reduction. It can also keep your Puma packs alive in a big push and if they get blown up? who cares you can call in more.
As a bonus the coax on the Puma can be a danger to snipers so if your getting bled by one just shoo it off. Oh and you will be floating shitloads of muni because you don't need to spend any on upgrades (because your using infantry that just come with them for free). I can't understate the value of being able to instantly replace losses when it comes to keeping map control.