They are not at all the same. In the slightest. A strap-on dildo is not attached in the same way a penis is, it doesn't have the same texture, it cannot ejaculate or get an erection, it cannot move organically, it is a piece of plastic - not at all the real thing. I am not going to suck or jerk off plastic, thank you. I wouldn't imagine it would be that interesting or stimulating for the woman either. And plus, the vast majority of gay men want (if not require) a man attached to the penis as much the penis itself.

There seems to be this weird "thing" in the TQ+ circles to justify gay men sleeping against their sexuality where they believe that gay men either only care about the dick, and thus should have no problem sleeping with MtFs or women with a strap-on. Or, that they only care about the man, and thus should have no problem sleeping with FtMs. Can they not understand that it is, in fact, both?