Am I in the wrong for feeling like my male experience is being "appropriated" here?

No, what they're doing is offensive and slimy, especially given the obvious sexual component to them fetishizing boyhood.

But I don't see how this isn't exactly the same as what MTFs do to women.

It's exactly the same as what MTFs do to women.

I'm kind of expecting to be told that I'm not allowed to feel hurt because women have it worse in society and what MTFs do to them is therefore "worse."

I won't blame a woman who pretends to be a real man to get away from sex-based oppression - not to claim manhood, not to talk over men, not to invade male spaces (especially gay male spaces!), but to do something both men and women should be able to do in a fair world.

However, it's not what these women are doing -- they don't hide the fact they're female (FTM, so female) but claim special insight into the male experience for no purpose other than degrading real men. This will never be not offensive.