Going at this in one go.
Wildstar and Darkfall were hard though from the start and the argument is that a game has it's difficulty increased. Aion and Lineage both also could be argued to have gotten easier (or more new player friendly depending on your point of view). I'd also argue with you till the cows come home that Wildstar is not unpopular solely due to difficulty, but that's because I personally view the game as having multiple major gameplay flaws, lukewarm story and a poorly conceived endgame. I've played the damned game enough to know that it's about as typical as an MMO gets barring the slippery slidey movement.
Coincidentally did you know Terraria supports up to 256 players per server? You won't be able to get that many on a run of the mill home pc for sure, but you can on a powerful machine. Say the same type of server they'd use for Final Fantasy? It's certainly no typical MMO type, but it has the required number to be considered alongside it (if we're getting pedantic about things). Also fine I relent that expert is optional. Though then I point to hard-mode through defeating the wall of flesh. The game play arguably shifts to a higher gear at that point.
In terms of games becoming more difficult rather than easier I was more so arguing in general. I'm ok if you want to point to any game not in the same genre that does it. I'd certainly like to know about it and the effects it had on it's player base. And no I don't mean something like nerfing an aspect of the game that makes it harder. That would fall more so under just modifying a game and how a player may disagree with the changes and is a whole other can of worms.
I don't remember saying that all players eventually reach the same skill (a skill cap). Not everyone is going to reach the same skill level, but everyone will be more skilled after starting than when they started and will continue to progress in skill. Even if the progress seems minor or insignificant.
Lastly, I want to point out that I'm not defending the OP's opinion in it's entirety, just some of it. I, for example, abhor the removal of skills, but I'm totally for being able to do old dungeons/trials at max level. I'm ok with them becoming obsolete and 'removable' from your bars to make things easier on players, but I believe that it's a horrendous waste to simply remove an ability because fitting all the skills on the bar is too hard for some. It really raises the question of 'which skills are on the chopping block for the next expansion?' and a skill effect/animation can be quite enjoyed and missed. I'd sooner the skills simply be there, but be pointless than to see them vanish. But this isn't quite so much about difficulty per say even that I argue. More so that I am saying that if the difficulty being lowered is the cause of the skills being chopped, I am against it. How long until my favorite ability is tossed because 'it was too hard to use'?