Hussar
Legend
Bounuses are bounded, so the range of meaningful DCs is limited, once you get to setting a DC, that is. By the time a DC comes into it, the DMs already made one ruling, in calling for the check at all.
So, yeah, rulings not rules.
But, again, that's not any different than before. The DM always had the option of calling for a check or not. And, in 4e, the DM is rather encouraged to only make checks when it mattered.
Look at the evolution of jumping.
In any edition, the player declares that he wants to jump across a 10 foot gap. In AD&D, the DM basically set any DC he felt like - there were no real guidelines at all. In 3e, the jump check DC was dictated by the mechanics, but, if the PC's skill was greater than the DC, then no check was required - it automatically succeeded. Same in 4e. Now, in 5e, there's no check at all. The PC jumps his Str score (presuming a 10 foot running start). The DM has no real say in things at all. Player says, "I jump X feet" and he does.
I honestly think you're overplaying this hand. Rulings not rules refers to 5e's backing off the notion of "Rules for Everything". But, that doesn't mean that it's not still pretty solidly a rules heavy game with rules for most things. It's not a case that 5e is somehow rejecting any rule set. In fact, I find that 5e follows 4e rules philosophy pretty closely - basically the notion that rules absent is not the same as rules light. 5e DOES have a rule for pretty much everything. It's just in the corner cases that 5e largely diverges from 3e and hews closer to 4e in having rules that work most of the time and then relying on the DM plus a healthy dose of guidance to cover the rest.