5e is DM empowering because it gives permission for the DM to use Rule zero (which both later 4e and 3e also gave explicit permission to do irregardless of whether people chose to or not)...
No, not even close. Rule 0 was a token acknowledgement of an inevitable fact of gaming: that the GM could choose to change the rules of the game all he wanted, no matter what the game said about it. Nothing else about 3e particularly encouraged or required DMs to actually up and change the rules, nor did the rules design-in DM judgment the way 5e does. Really, no prior edition has gone as far to insert DM authority as unambiguously into basic resolution as 5e (1e was darn close). It's not a dramatic thing when you look at it, it's perfectly reasonable, but its tremendously DM-empowering because it does establish, in every action, that the DM is going to decide on the results, that the rules are not deterministic. 3.x/PF, in stark contrast, has rules that feel pretty deterministic, and the community attitude at the time leaned even further in that direction. I mean, it brought us 'RAW' vs 'RAI' and the Oberoni Fallacy. 4e may have been less deterministic with it's openness to re-fluffing, but it was still easy for the DM to just let the rules do the work - 'easy to DM' in that sense has been likened elsewhere to 'empowerment,' but that's like saying a Segway is good training for a marathon.
It's not player empowering because abilities (except for spells, class abilities, so that leaves skills??) don't have objectively defined...mechanics (those are there)
Just defined. How do you answer the question 'what can your character do?' In 3.5, you parse the rules text and determine RAW. In 4e, you check the rules text, and maybe tweak the fluff. In 5e you describe your action to the DM and find out if it works or not. The former two are 'player empowering' - and lend themselves to all manner of powergaming shenanigans - the latter is DM Empowering.
DC's for every action that can be taken with the skill (No edition has this)?
3.5 did, and 4e had level-based guidelines.
DM adjudication of DC's (every edition had this)??
In the same sense that even a game that didn't acknowledge rule 0, in fact had rule 0. But 5e goes further than just adjudicating DCs, the DM doesn't even need to call for a roll.
What exactly and specifically is being called out as dis-empowering to players in the mechanics of 5e?
Maybe it'd be easier to see as 5e "eliminating player entitlement." 5e did have some design decisions that were trade-offs rather than unalloyed positives for everyone (really, 'most all game-design decisions are like that), fans of 3.x/PF or 4e/E could come up with some good things about player empowerment that they miss in 5e - and have done. Those same things are often the flip side of a 'player entitlement' coin that has been cashed in to fund DM Empowerment, instead.
I've been trying to be 'fair and balanced' in all this, but it seems that using the term 'player empowerment' is getting in the way. Let's just call it 'player entitlement.'
5e 'Empowered DMs' and 'eliminated player entitlement.'
It is possible to say that every choice is viable, but then mechanical balance becomes rather meaningless as well. Making sub-optimal choices was very possible
'Sub-optimal' is not the same thing as non-viable. Viable is half the definition of balance I like to use, the other half is 'meaningful.'
A balanced game presents many, meaningful, viable choices.
5e presents fewer choices than 3.x/PF or 4e/E, but each of those choices is as viable as the DM makes it.
This is actually not valid. RAW, a PC did not really "get better" at things through leveling because of scaling DCs, and defenses.
A common, if bizarre, misconception. DCs for the same task didn't change because you leveled - you might tackle more difficult tasks, though, now that you have the ranks for it. In 5e the same task might succeed or fail or call for a different DC, whether you leveled or not, that's up to the DM.
There is a huge difference between not continually boosting a stat and "dumping your prime requisite."
You need your most important stat as high as possible. If 'as high as possible' is 20, putting an 8 in it is certainly dumping it - and, if 'as high as possible' is 25+5 inherent+6 Enhancement, a 'mere' 24 is just as bad.
No, not "silly", I saw intelligent people make a fighter and think that since they were proficient in it, they would be reasonably effective with it.
'Reasonably?' For certain definitions of 'reasonably' sure. ;P It's no different from using a STR weapon when you're a DEX build. And, yes, that was silly - based on a preconceived notion that no longer applied. It'd be like expecting a 5e Ranger not to cast spells at all (which, people did), even though a Outlander Fighter would cover the same concept.
Even still it isn't true, as making suboptimal choices, like diversifying your character or not taking the right ASI or feats will cause you to take a huge hit to your effectiveness.
That's all relative. Being 2 points 'behind' the theoretical curve, whatever that might be, is like a -1 to hit. It's a hit, but not a huge hit.
If anything, the abandonment of formal Role/Source, and reduction in non-casting/non-magical options further illustrates the point... that martial/spellcaster classes is a false dichotomy in 5e.
So, what, non-casters have been erased? No one should want to play one? Those who do don't deserve choices? Absurd.