The ol' PR public apology formula is:
1) Acknowledge
2) Apologize
3) Make it Right
4) Recommit
He kinda already failed step 1 and 2. He didn't really specifically acknowledge what he said, just vaguely said "I said some dumb things when i was younger and no longer feel that way". He kind of apologized, but not very earnestly, which granted is very hard to do when this stuff is thrown at you.
If he had gone out there and said "I'm sorry for using the n-word, my sexist remarks about women, and my homophobic slurs" then said something about "I'm actually now a champion for gay rights... etc." then it might have worked, but he's 24 and no PR expert.
I'm kind of blown away that his agent or the Brewers don't regularly do a social media check and scrub stuff like this away. It should not have come out this way.
I will also add that I had a Facebook at 17/18, and knew not to have anything controversial publicly available, and this was in 2007 (I'm 28, Hader should have known better). I'm sure I said stupid crap in high school that would be embarrassing to have a record of, but 17 year olds are smart enough to know it's wrong (in general) to think those ways and definitely wrong to tweet about.