Just like those restomod muscle cars, each one is a take on what the owner/builder likes and liking different things is part of what makes that whole scene so much fun! The QRF rail is definitely stiff and it would resist heat buildup much better than most modern M-lok etc sorts of rails, so if you're going to run through a half case in an afternoon that'd be a lot more pleasant to work with for sure.
You're right, though, in that a quad rail is basically retro at this point. Crazy how fast this stuff is changing!
Not long after I made that post, I was killing time on BCM's website and found out they offer a 14.5in middy with an A4/M4 style FSB and a few different free floated rails, so now it's likely I'll be buying a matching pair - one for me, and one for my prior-service wife who thinks any AR that doesn't have a traditional FSB 'doesn't look right'. Those plus pin & weld jobs with the appropriate suppressor mounts for a decent can.. heck yeah!