@Nav's Heavy armoured exoskeleton idea
Do note that anything I say is very possibly inaccurate, simply due to the randomness and luck inherent to Tinker. PW almost certainly doesn't remember how hex composite works, so thinning it could actually work exceptionally well, if you're lucky.
That said, you're probably better off just using battlesuit plate instead of thinned hex composite. Most weapons fall into one of two broad categories: weapons which have a hard time breaking one layer of BS plate, and weapons which can quickly break all five layers with ease. There's exceptions, like the HEP, but most weapons fall into one or the other. Hexcomp is made to take advantage of this, by using one layer of BS plate (becoming temporarily immune to the former category), and two layers which are nearly immune to either kinetics or energetics (becoming highly resistant to BS killer weapons, and completely immune if only kinetics or energetics are being used).
Thinning hexcomp would probably degrade this effect significantly, because you'll still die quickly to BS killers, but won't have nearly as much resistance to small arms as BS plate would grant. You'll retain immunity to certain types of BS killers--anything laser, and anything shard--but stuff like energy projectors, plasma, and HGCs will still ruin you.
So using thinned hexcomp is much more of a tradeoff; You might have something like 50% better resistance against BS killers, compared to having just two layers of BS plate, but you're going to have significantly worse resistance to small arms.