In Pf, the DC of checks moves relative to the party - as you said yourself, a moderate challenge is represented by a 15 at low levels, and by a 30 at high levels in Pf. This is NOT the case in 5e.
This means that your comparison is not balanced.
Somewhat. While technically, yes the definition of "moderate difficulty" checks in 5e doesn't increase, in practice it would. Higher level 5e characters face higher level monsters, who will have higher stats and PBs. E.g., a 5e goblin's passive stealth is 16 while a Vampire's (CR 13) passive stealth is 19. This is why I slightly increased my high-level typical/moderate DCs even for 5e. Though I admit this only necessarily holds true for contested checks and remains a much small difference than in PF.
Phrased differently, high-level 5e characters should typically be dealing with "hard" or "very hard" checks, while PF's system scales so that the term "moderate" is ~equally applicable to all levels of play.
Originally Posted by Niara
The bonuses are plenty potent enough in 5e's system, and they absolutely do NOT need to be any higher. You can definitely build your characters to be effective and skilled at certain things, already. The skill progression in 5e is good. It's Meaningful. I far, Far prefer it to other previous systems.
Like Pathfinder... where you will frequently have characters who will drown on still calm lakes because they didn't have the spare points to put ranks into their specific "swimming" skill, because they needed those skill ranks for other things that actually made them effective in their role, like stealth, sleight of hand, disable device, perception, bluff - you know, the ones that matter... but since they didn't 'waste' ranks on 'swimming', they now will drown on calm placid lakes on sunny still days, if they try to take 10 on the swim across it. Such a great system I don't think, thanks...
To be clear, I'm not arguing for a Pathfinder system of craziness. I would like some compromise between the two systems, weighted more towards 5e. Where 5e players can both manually allocate points to improve skills (this part especially), and doing so can result in a slightly bigger (~+15 at level 20 instead of +11) bonuses. Or you can spread out your points to be more of a jack-of-all-trades. But I also understand why people wouldn't want this, and I totally agree that the pathfinder system can be messy/frustrating/dumb.
p.s. I'll again link this to ST progression in 5e, which I think has the same problems but even worse. Enemy DCs go up and failing to save against a spell is typically much worse than failing a skill check.