Respectfully I feel you are being particularly unfair in this instance.
- In the conversations with Lena it appears clearly that there was a woman, the project of a family and maybe a baby a long time ago, according to Seymour.
- Seymour hints on several occasions that there is a secret reason why he is so obsessed with Lena.
- Lena's Dad is only her stepdad, her father abandoned when she was very young.
- When Lena meets Seymour, she does think he looks particularly familiar, and she does not know why.
As for the "patreon point", everyone seems to forget that a lot of facts that look canon in this game, are actually not. It might well be the case here.
Just as, according to your choices, Jess might be with Dave, with Ash, or with no-one, maybe we will come to realize that, yes indeed, if Lena does sleep with Seymour then he is not her dad, but that if she does not, then yes he is. Patreon problem solved.
I have the same pet theory about Mike's girlfriend for example. It would certainly not surprise me that Mike's girlfriend is Gillian only in the case of specific choices you've made, and that with other choices it will not be her.