Could the brutal picks stand to be made a bit less "hyper specialized"? Probably.
This which would actually make the brutal picks a bit more effective individually, but the less specialized they are, the more the "boost" of "effective utility" by having multiple kinds will be polynomial rather than exponential. So each individual one may be more threatening, but as a whole, a group of less specialized ones would actually be less threatening than a group of highly specialized ones.
But I don't think the idea of how the AI HW defenses work is flawed. Just some of the stats need tweaking.
That said, there is only like 1 or 2 brutal picks on difficulty 7, so it isn't all that bad even if you get a pair of picks that complement each other well. It's only at around 8 or up where you get enough brutal picks start being able to shutdown everything.
I will point out once again that humans "ultra stack" defenses all the time, so it only makes sense the AI does so as well. They just got a "head start" on it because, well, they won the war.
I still feel like fortresses need a similar treatment to be less "send polycrystal units in to slowly grind it to death"-ish, but that is another discussion.
(Hint for the fortresses + superfort + forcefields, transports filled with polycrystal units. The transports will let those polycrystal units get close enough to at least get some shots off on the forcefields)