Has the game become too Raid-centric and basically made raiding and with legion dungeon content the only real relevent end game thus far? Yes.
Has it become casual friendly? Hell no.
Wrath was Casual Friendly, you had a difficulty curve "just" hard enough that there was a challenge, but it was accessable and community welcoming allowing people to actually join raids for the first time when TBC was "exclusivly" 1% of the playerbases playground at the expense of the 99%.
You want to blame anything on the problem? Blame raiding, we have 4 tiers of difficulty because heroic wasnt hard enough for an angry minority and LFR wasnt easy enough for a lazy majority, neither are right, both, are wrong.
We dont need 4 difficulties of raids, or 5 tiers of god damn Dungeons.
Normal dungeons, were for leveling.
Heroic dungeons, were for gearing.
Normal raiding, was for casuals that liked doing normal difficulty content.
Heroic raiding, was for hardcores, that liked difficult challenging raids and wanted to actually suffer to get the best victory.
"That" was the best god damn system WoW ever had and frankly we have abused it into oblivion with Mythic and Challenge Mode bullcrap which has honestly done ALOT more damage to this game than helped it.
The "catering" is a load of bollocks, the real issue is that two very specific groups are to blame, the far left who dont want ANY challenge and want to be rewarded for sitting in a Garrison, and the far RIGHT that want content ONLY they can access and nobody else has a claim on it.
You are both the reason this game is dying, theres no casualization, the issue is, "you".
Theres a good portion of the player base that wanted a easy/normal raid difficulty that was just hard enough that it could wipe you, but easy enough that you could learn it fairly quickly and play it mostly for fun. That group is completley ignored because we get told "normal" (which is basically difficult only because of a gear wall) is our difficulty curve now.
We've had to be content with that for 3 god damn expansions now, and a 4th one is comming which will yet again constantly screw up the wheel by adding yet more difficulties, and yet more pointless content for the pointless people.
Why even BOTHER doing heroic dungeons anymore when Mythic is CLEARLY going to be the focus of end game raiding?
Why even HAVE A mythic mode when your clearly adding a new version of Challenge Mode for those looking for actual difficulty?
What, is, the god damn, point?
Its no wonder, people get burned out of content when they are repeating the same damn raid nearly 6 months with "nothing" versitile to offer the game at all, no pvp, world pvp, no world pve content that actually gives relevent progression outside of raiding and dungeons.
No crafting content because all the crafting is blocked by pointless trivial "only 3 pieces per character" bollocks which honestly trivialises using it as a progression at all. The game offers you "one" road to the inevitable path of raiding, do anything that helps you get gear, for raiding.
Raiding, is whats killed this game, not casualization, casualisation is what gave it a damn 12.5 million subs during Wrath, when things were exactly as they should have been, world content, dungeon content, raid content, pvp content, and crafting content, were, relevent.
Everyone had "something" to do.
Thats the problem, not this bollocks on the game being too casual, not the rubbish that its not hard enough, but the fact that theres two audiences that just cant be pleased because both are as malcontent as the other which makes it literally impossible to hit a middle ground.
What the game needs to survive is a return to the old 2 tier difficulty system so that "other" content can get attention than raiding and dungeons.