that is the exact reason that people use addons, it essentially gives you the exact same information but in a much more readable manner. that is the main issue that most people have with the default UI, all of the important information by deafult is pushed out to the far edge of the screen, meaning its a lot more difficult to be able to keep track of everything and not lose track of your toon
generally if you are doing the more difficult content then you do get better gear from raids than you do from dungeons, even from doing 10s which is teh current highest item level for dungeons,
and there are some differences between dungeon mechanics for normal-heroic and heroic-mythic, to give one example, on the totem boss in atal dazar you can just kill the totems whenever on normal, but on heroic you have to kill them all within a few seconds of one another or they reset
there is also a very good reason they got rid of tier sets, they were an absolute nightmare to balance correctly, it would be nice to have the mogs available to players still but tier sets are not a good design anymore, unless they put it back to 5 pieces and didnt make them stupidly strong buffs
if there was only normal and heroic then they would have to set heroic to a specific raid size, like 20 man for example, this would mean people just complain about that, it would need to be a specific size in order to keep balance going, otherwise people would complain about certain bosses being stronger on 10 man than 25 man and vis versa like they used to.
its kind of difficult to claim its unfair, considering that all of the information that you claim are training wheels for people is also actively available for you, you just happen to chose to not use it, it would only be unfair if it was available to specific people and not others.
all of this information is available to everyone, all you need to do is read up on spells and learn they uptimes and cooldowns and you know exactly how long a cooldown will last based on its visual and how long it will be on cooldown, so realistically you are just complaining about people chosing to show this information in a way thats user friendly
but as someone has already stated just because someone has information it doesnt mean that they are able to use it correctly, so there is still a level of skill required in order to be able to complete any content
we already do, thats the point a lot of people are trying to make, just because addons exist it doesnt mean that they are bad, it just means that its the way the game works