Some things I do not like.

[Lelila38]

I disagree. Simplification doesn't necessarily equate to "dumbing it down." That terms is also a little demeaning. I'm not dumb. I just have certain physical limitations. Another caveat here is that not everyone plays for a challenge. While some do find challenge fun, others don't.

Then there should be content and classes in the game to suit both.
As others have said, you don't have to play every class. Stick to one and focus on learning the basics. If you play casually there's no need for you to optimise and min-max.
Pick one that resonates with you and whose style you like. An important part for playing with physical limitations is setting up the UI in a way that suits you. In xiv every element can be adjusted in size and placement. Don't be afraid to experiment with different setups. I believe someone mentioned using a controller, do give it a try. The buttons might be easier to reach for you.
You mentioned most classes have too many skills. Mighf I suggest you try out dancer? I feel like there's not a lot of buttons to press there. Another class to maybe have a look at might be Red Mage. Both are very fun to play.