That can be a very elitist way to look at the situation. Maybe the healer is new to the game, maybe they're new to healing or new to their job. Maybe they just rearranged their keybinds and are just getting used to them.
Saying "not my problem" isn't going to help matters. Maybe instead of encouraging the "you suck, I'm great" mentality, you should encourage him to talk to his healer and figure out why the healer is struggling and figure out a work around together.
And don't give me the "if you can't handle wall to wall then you shouldn't be there" schtick. Slowing down to accommodate another party member isn't going to kill you. Most runs take between 15 - 25 mins depending on the dungeon and comfort level of the group. You signed up for this. If your run takes 20 mins instead of 15 it's really not the end of the world.
OP isn't positioning himself back in front of the boss after a mechanic; which likely means he's not very practiced himself. It might not all be the healers fault.