It isn't about look only. BTW consider the point that Triss loves Geralt without any genie bussiness, And hey so Yen could magically change her appearance and Triss didn't? Let me remind you that in some cases Triss could beat Yen in magic. That is why Triss was in Lodge, invited as a recognition oh her power. Yen never was invited.
Triss is infatuated with Geralt, she wants what she cannot have and enjoys the affection of Geralt. In the books, when she is a POV character, he thoughts are physical and not romantic. Her Witcher 1 personality was emulated Yen to manipulate Geralt in his amnesia, either that of CDPR completely messed up her character.
Yennefer was invited, but not by Eilhart. It was Francesca Findabair who was allowed to allocate two seats (Ida and Yen). The Lodge never recruited for power alone, it was a political organisation first and a magical one second. Philippa did not invite Yen due to her personality. Yen was of equal rank to Philippa being on the Council of the Brotherhood of Sorcerers, Francesca being the only surviving member of the Chapter was above them - hence the two seat bribe that Francesca used to get one up on Eilhart by inviting Yen.
Triss has a lot of potential but is very inexperienced. She is incredibly powerful for her age, but think how much magic she taught Ciri at Kaer Morhen compared to Yen at Ellander. When Triss reaches 100, I'm sure she will be better. But right now, she stumbles into power - her famous Merigold's Hailstorm spell was a miscast.