The Puma has a very clever penetration profile. Its far penetration is a very light-vehicle esque 80, but when it closes within 10 metres of an enemy tank (about the length of a medium) its penetration spikes up to 160.
This lets the Puma scale into the mid and late game better than any other AT light: rather than just becoming useless, it can continue to deal damage by getting dangerously close to the enemy.
Should that be extended to the Stuart and AEC? The AEC is pretty much a Puma clone but only has a near penetration of 120 despite facing more heavily armoured targets. The Stuart has awful penetration, rendering it pretty much useless after the light vehicle phase.
The Puma is super squishy you got to take that into account. It's can do stuff but it's still no tank. OKW puma is pretty damn good though, but once you vet it. Yes it's aim-shot is nice, and it can do stuff to things, to counter act it though it's a long wait time, or that's how i feel, But like with all OKW stuff, when vetted, they do stuff, lots of stuff.
As for the Stuart, it needs something going for it. I'm not going to lie, it's pen values are kind of trash, though it can be a thorn in the side of lights, and sometimes mediums.
As for the AEC it has the better snare and probably in a good spot. I wouldn't want to change it as of now. I can use it no problem all game around. and it can harass the opponent so much, i had people throw stuff to try and kill it.