You're assuming OP's situation, man. What tells you that OP isn't working on it and improving?
OP is making post about meeting other cosplayers, they're not promoting obesity or anything. Do you see smokers in the street and tell them to stop smoking and make fun of them? You don't, just because you're behind a screen doesn't mean that you can be an jerk to people minding their business.
And about your health condition improving, good for you, really. But you cannot apply your situation to everyone and assume stuff about them, you know? Not to mention that your original comment, which was deleted, was straight up mocking OP. Coming from someone who got bullied for their weight like you said, I thought that you'd have more sympathy.