Yes, well, that's an entirely different (and equally legitimate) reason not to like him.
I like him because he is so over the top ridiculous. I'm not terribly offended by his Mary Sueish ways, I think they're hilarious (particularly because he is SUCH a dumbass, despite all his abilities and talents). A lot of characters in Batman are Mary Sues, most of them have simply grown out of it. I like to assume that Damian will eventually develop in a nuanced and meaningful way, but I have a lot more patience for that sort of thing than most*.
Though I certainly agree that he needs to interact more with the rest of the Batfamily, particularly Cass. She has the ability to put him in his place pretty quickly, both in terms of her fighting prowess and the fact that she has a background similar to his and could offer genuine insight (if she so desired). She was also raised to be a weapon and treated less like a person than a means to an end. The methods and the results were vastly different, but ultimately he has more in common with her than most.
I get that there are a lot more reasons to dislike the character than like him (both in terms of characterization and at a more meta/critical level), I'm just willing to be that annoying person who champions him because I think there's a worthwhile character in there.
*Not that a high tolerance for bullshit and questionable writing is something to brag about