I agree, and think that that is what most people would think was meant if someone announced that they 'had sex last night'
well those people would either be lazy or not very bright, wouldn’t they, especially if they knew that the person was a gay adult female? And, crucially, they'd know they were being lazy.
And it's not really a different discussion for you though, it seems, since your use of the word ‘misleading’ introduces some sort of moral note into the mix which really doesn’t belong here as no one owes you an account of their private sex lives. Would you like us to say, ‘I performed a sexual act last night and had it reciprocated’? It’s very clunky isn’t it, almost makes us not want to even talk about our realities at all and stay invisible. Let's see, what's more colloquial, at least halfway accurate and not 'misleading'...should we say 'fooling around'? Your sex is Real Sex but my sex is just inconsequential messing about?
More generally, the very act of asking the meaning of a word in this manner confirms that there is no consensus supporting it, and so you necessarily do from that moment invite discussion around what 'ought' to be, because language-use is structured artificially wrt the zeitgeist. The two can't be separated.
To return to your (alleged) first point, I'm saying that many people are not straight and as such will only see PIV as one sex act among several, thanks to efforts made to increase LGB visibility. It's not the 90s anymore. While we clearly have progress to make, given today's climate, I really wouldn't be so confident in arguing that most people are so loyal to such a strict definition of sex.
(It does already have a distinct term - PIV - and sure, give it all the additional names you want, just as long as plain 'sex' isn't it)
Agree stripey