I think a lot of this is Mikey's status as the baby of the family. He does have high empathy, but because his brothers largely go along with what he wants and shield him from the consequences of his actions, he can be careless in the way he treats people. Basically he has the expectation that everyone will give him the same grace as his family, and doesn't necessarily notice when his actions are hurting others.
He's used to being literally carried around by Raph (no issue to Raph, since Raph is 3x Mikey's size) and sometimes Leo and Donnie, so he doesn't see a problem with expecting Todd to carry him, even though Todd is clearly struggling. On the other hand, as the youngest, he's usually in the position of *being* excluded, and doesn't think he's capable of excluding others, which leads to him not thinking twice about ditching Todd.
Dr. Delicate touch is basically a function of his brothers being much more gentle with him than he is with them - he doesn't experience the same consequences for speaking harshly, even to people outside his family - his brothers always try to shield him from the consequences of shooting his mouth off. Which is sometimes valuable - it gives him the power to speak up, even if he's not tactful.
