what is the "WWE style"

The miz is the best example of a WWE safe style wrestler. He was one of the first wrestlers to start doing it when he was in developmental, has never been on the disabled list and looks to have 25 years of wrestling left in him.

The way i see it is pretty much everything you mentioned.

Some other things i can think of to add

Pacing
- WWE has its own style of pacing you never really see anywhere else. I'd say that's mainly to cater to the 'WWE audience'. Obviously WWE Audiences are largely kids, families & 'casual' fans, people who wouldn't necessarily be able to keep up with the over the top, fast paced action & know everything that's going on. So the slower pace with a lot more rest spots & character development gives them more opportunity to take in what's happening and process it, telling the story a lot easier for them.

Hard Cam & Angles
- Almost every wrestling show anywhere will have a hard cam, and you'll logically work to that cam more. Though with WWE, you have that & 1000 different angles to try and work for, as opposed to maybe 1 or 2 cameramen you'd see on an indie show. So i'd imagine you'd have to learn where they usually are, and how to sell for them during the match.
Another thing with the Hard cam. I'm not sure if a lot of other companies do it, but in WWE the face will usually always be in the corner closest to the stage & the heel closest to the time keeper, at the start of the match & in tag team matches. I'd say this is so the viewer can see the face & see their expressions, where as the heel will have their backs to the hard cam. 

Promos
- Memorising promos would be another thing. You're following 'the script' in WWE, rather than going out there and winging it. Obviously few guys get freedom on the mic, but they're mainly the ones who have proven they can go out there and cut a good promo without fault. WWE is big on production, so they wouldn't want everyone going out there and trying to cut promos off the top of their head, with some not knowing what to say, then making themselves look stupid on live TV. They'd rather you have that script which you can likely remember and go off, so you've at least got something to go out there and say.

Social Media
- More now than ever, they've got to learn how to manage themselves on social media. How to act, what they can & can't say including the banned words list, how to promote what they're doing etc... A lot of people still keep some level of kayfabe on social media, one example: Dexter Lumis, he posts a lot of every day stuff, but he still shows his character in them.

Some people take to the style change well, and others don't. Some need development and some (in Styles' case) don't. I guess that just comes down to how well they can work with specific guidelines, or a lot of freedom. In Zayn & Joe's case, i'd say they've adapted perfectly fine, but injuries & perception of them are the only things holding them down.

Shorter matches, entertain, follow the writer's story, your "finisher" is your most powerful move, play to the crowd, big usually beats small, you have to have "the look", get in get out so the next match can happen, you're on TV not in a bingo hall.

Whatever Vince wants it to be.

the ‘wwe style’ is largely aged out now due to the work rate revolution that occurred in the mid 2000s, early 2010s. hence the rise of punk and Bryan and immediately after them more indie talents finding success.

talents like Mr Kennedy, even Cody Rhodes when he first started, Carlito, Chris Masters, Trever Murdoch, Miz, generic dude in tights and a nice hair cut #1000, la resistance...

guys that looked great on a poster but were never gonna do a 450 splash and probably would be bad at taking one, too. guys that were decently athletic but were not the caliber of athlete that is the new standard in today’s wrestling.

that’s very summative on my end, but that’s the gist of it.

Storytelling, reading the crowd, not doing unnecessary acrobatics when unneeded

I always considered the WWE style to be more focused on the cameras and production. Like making sure you’re hitting your mark for a key shot, working facial expressions, talking more in the ring, giving the announcers more time for exposition, etc.

you guys are forgetting, work the left side of the body! LOL

Always think of "Less is more". Not too many flashy moves unless on ppv or has a meaning.
Also another thing is getting used to the "WWE style ropes" they tend to be more looser. Knowing how to pace your self in the 20x20 ring. Not many wrestlers are used to the ring size before they get to WWE.