A few thoughts in response:
-- Yes, this is a total retcon that discounts some stories that have taken place. I also tend to not like those (as you say, I also tend to prefer the ones that "takes place between the issues and between the panels") but for me this didn't contradict anything that was particularly important that has happened in the past. Not anymore than the various tweaks to GL power ring abilities have in the past.
-- I don't think it's about some special "yes or no" qualification. (not like midi-chlorians in the blood) Ollie and Barry were both able to use it - it just took a lot out of them. And I would think that's also where the training comes in. The fact that GL's undergo training and a boot camp was a retcon as well, and it was one that made sense - that it takes practice to muster that much will consistently. That doesn't negate the possibility of someone taking control of a GL ring (they've been hacked 3 times in the last few years) if they have the willpower, or of a GL having to prove themselves without their ring - those stories can still happen.