Both the REC7 and the LWRC are quality rifles. I have seen the REC7 lay down some nice groups, no so much for the LWRC, but both are high quality, very reliable rifles.
Both rifles will shoot steel case ammo "fine". The issue with steel case ammo is, it tends to "stick" in the chamber when you get the rifle hot (hot as in, high volume shooting).
I don't understand the "AK reliability" question. That's pretty much a myth and chatter from the uneducated/uninformed. To be clear here, a quality AR is just as if not more reliable than an AK.
As far as DI and a piston rifle go, I have and shoot both. Honestly I don't have a preference, I simply cant tell any real measureable difference in the way of reliability. Yeah, there is more cleaning involved with the DI rifle, it's just a non issue with me.