Armalite has no more or less to do with AR-pattern rifles than any other current manufacturer. Their "AR-10" is not the same as the original. (None of them are.)
(I hadn't heard Armalite was bending and making a rifle to take the KAC mags.) Armalite made a calculation when they released their .308 rifle during the AWB. They figured that if they made it compatible with magazines that were plentiful and cheap and could be modified to be used in the rifle, thereby not getting stuck with a rifle limited to ten rounds. When the AWB expired, no one else thought this was a good idea. KAC designed their own rifle, which DPMS and POF have also picked up on, using the same pattern. Armalite made a diagonal cut on the corner joint between their upper and lower that few, if any other manufacturers will match. When the military bought the KAC pattern for their SASS rifle, it instantly became more accepted and standardized. When Magpul started making magazines for it, my last concern went away. (Their market domination is evidenced by this news of Armalite accepting this pattern of magazine now. I wonder if they will also retire their proprietary cut and just be compatible with everyone else.)
There is absolutely nothing wrong with the DPMS rifles. They are very reliable and sub-MOA accurate out of the box with match-grade ammo. If you handload for it, remember, you need to full-length size, not just neck size them.