Does "doing the same to cis women" ALWAYS justify doing it to trans women?

When I asked here, that if it is OK for a guy to voice trans women, most of the replies told me that it is indeed a bad idea. (Said post is deleted now)

However one of the replies asked back if I was going to voice cis women myself- and I probably would have if I had voiced the trans woman myself.

But, here's the thing. Would me(a cis guy) voicing cis women justify me voicing trans women?

Here's another question: Does drawing a trans woman whose passing is very reliant on her breast size (By that I mean masculine and/or androgynous face) become justified if I drew a cis woman who is like that?

I know, that generally, if you would treat trans women the same way as you would to cis ones, you'd be A-OK, not a transphobe.

(Same goes for trans men and cis men)

But does that rule ALWAYS apply? Like, even in the aforementioned two situations?