Yeah, this is one of those 'excuses' to make women attractive that frequently come up and just because the novels did it too doesn't make it any less...tiresome. Women being 'powerful' because men find them attractive is a very worn-out trope in my opinion.
I'm not saying whether it's right or wrong. The books just depict a very imperfect world and sorceresses use whatever edge they can to get ahead. I'm just merely explaining why they are generally very attractive. Not every female in TW2 was as sexually appealing as Triss or Ves, but then again most of those weren't major characters either.
Triss is a damsel the whole game, Phillipa gets locked up, tortured, and needs to be rescued by Geralt, Baroness LaValette is tortured (naked) and needs to be rescued by Geralt, Sabrina is burned alive on a wheel, Saskia does the whole sleeping beauty routine and needs to be cured by Geralt, Vess is raped and needs to be saved by Geralt, etc...and all of them are wearing sexy clothing. The game portrays them as damsels and objects of desire. No thanks.
Triss is really only out of the game for the second act, being a third of the experience. Phillipa is far from a damsel as she calls upon a dragon to ravage and destroy everybody in the third act. While the Baroness was topless, so was her son if you decided not to kill him in the same exact scenario. Sabrina massacred an entire battlefield because of her choices and hardly was innocent. Saskia potentially smacks around King Henselt, depending on who you side with.
Ves was Roche's strongest and most reliable solider and only found her match to be that of Geralt. The tragedy that ensued with Henselt was more to show how much of a scum bag he actually was. When someone says "sexy clothing," I envision lingerie. All of the characters are far from being naked. They are fully clothed, albeit perhaps stylish. My point is that TW2 depicts everything in multiple ways depending on your choices. You gave a largely skewed perception based on what was likely your only playthrough.