The 30% joke is because of her perceived contract with QC, not due to anything else.
The primary reason why this doesn't "seem right" is because we have never seen Dora on this end of a relationship - the pursued instead of the pursuer. What
really didn't help was that Tai's decision to go talk to Dora was made very suddenly, and after very little forethought.
The arc before all this was Marten training the interns while she was sitting back, getting high and watching
Adventure Time, for cryin' out loud. The only time it suddenly became Dora-focused was when she ended up back at Faye and Marten's place, and Dora came over. No buildup, save
a little soliloquy from her in 2214.
I think that if, in Tai and Marten's ensuing conversations, Tai would have been a little more revealing towards Marten about her desire to want to settle in to a monogamous relationship, it would have made a bit more sense.
However, she was a little bit over-hung after she made the decision - so it might be the wine talking. Which makes us all see this relationship as what happened to
Marten and Vicki. ("Life-altering decisions should never be made while drunk, dummy")