Hey grindfactor, I've been torn on it myself, personally. I generally just throw on any gear that I find as long as it'ss a higher Gear Score and adapt accordingly. But if there's ever a chance to create Brand Set synergy, I always go for that (sometimes even for a 2-5 Gear Score negative trade off.) It depends on how much you rely on your previous setup and how much you're willing to try whatever comes your way.
I believe Voodoobox, at least with his first statement, is referring to the 3 Gear Sets (Teal/Green items), not the more standard Brand Sets. (Please correct me if I'm wrong.)
My advice would be try just sticking to Gear Score, but if you're finding the content starts giving a bit more trouble than you're wanting, then start really focusing on Brand Sets again.
I hope this helps!