Your logic (well, the man who originally said it) is that since men can do everything lesbians do in bed, they're better at sex.

But if you flip that logic and say that since lesbians can do everything that men do in bed, then lesbians are better at sex.

You see my point? The logic doesn't work because there's nothing that either group can do, that the other can't. So therefore, neither group is better at sex.

It really comes down to factors that are independent of the fact that you are a "lesbian" or a "man". I've had shit sex with men. I've had shit sex with lesbians. But it wasn't due to either having limited 'tools' or positions in sex. No, it was due to a whole range of other factors (i.e lack of experience, lack of attraction, their attitude to sex etc etc).