Authenticity in this regard is a foolish idea. It can't be measured in any way shape or form. It's a promise of a snake oil salesman. No such thing can be seen in a person's life, cis or trans, gay or straight. The feeling of not fitting in is of course real, but manipulating teens at the height of their brain plasticity is always bad. Now then the difference between manipulation and guidance is debatable and political, but it's not anywhere near the mentally and physically broken messes of far left Twitter, and that's being charitable and expecting only pain without malice. (Like, we know the sentiments on the far right are malicious.)
If you want to make a philosophical point about the legitimacy of "authenticity", go right ahead, but we're just talking about pretty simple stuff most people take for granted: no decade-long self-denial, no hiding your partner, no lying about who you're seeing. No feeling of shame or repression as you hide from your parents. No getting disowned or threatened if you do.
That's what most people mean when they're talking about authenticity in that context. It's a life that the vast majority of straight people are able to live in modern western society. And if you're gonna argue against people encouraging gay kids to be more open in pursuit of that, then I find that more than a little bit grotesque.
Because we nowadays have little sexual morality, consensual sex can be summed up as "anything goes as long as both are into it". The pointlessness comes from heteronormativity reinforcing itself (usually everyone in the classroom is the result of a hetero-relationship). If "anything goes" just ends up repeating heteronormativity, then it is how things ought to be.
At its core, it seems that you're arguing that since kids are born as a result of heterosexual sex, therefore heterosexuality is the only kind of relationship worth teaching them about.
It should be patently obvious why that's utter nonsense. Firstly, not all people are straight, whether they're born to straight parents or not. Secondly, there's absolutely no reason that education should solely reflect what the kids already see at home. Why should it? Its purpose is to educate them on the world, and their own future lives, not just to tell them what their parents were up to.
Non-straight people are supposed to be normal people like everybody else. I admit that there probably is a point of disagreement hiding here, because if I were to be the professor I'd introduce intimate relationships foremost as families into which children are born and then expand from there, whereas how they nowadays say: two people form a relationship and it can be M/M, F/F, and F/M. But it warms my hetero-heart to know that kids interpret that as gay porn, porn, and real relationship.
If you actually do "expand from there", then that's not such a big problem. But you appear to be arguing for the exclusion of anything else.