Where do you see the "contrived" coming in? Is it the difference in personalities, or seeing Dora as not ready yet, or something else? 'Cause they've considered each other cute for a long time, and Tai's development into a more mature character could lead her to seek someone more like Dora than like her previous affairs.
I'll try and jump in on it but I'll likely get it wrong.
Here's what I think when I see "contrived." You have Marten and Dora going back and forth for a big portion of the comic before finally getting together. Dora is at this time the only character that isn't straight up hetero. They start their heavy dating and get really close. Then you introduce Tai as the lesbian character. She, in all her immaturity, makes not so subtle advances on Marten's girlfriend and pretty much says she wants to boink Dora and makes it none too subtle she's fairly jealous of Marten. Meanwhile, from my estimation there is a more sisterly vibe from Dora to Tai. Hence "cute little butch girl" and "not my type" references. I'll give that they had flirting instances, but all seemed playful from Dora's end and nothing serious.
Then you hit the Dora insecurity arc supreme and things end. Dora takes a break, then tries a date with Jim. Doesn't work. Therapy and boom. Out of left field Tai finally goes for it and Dora (who, in my estimation has shown only very friendly platonic feelings to Tai) figures what the hell. And you the lesbian character who couldn't keep the Dora salivating under control get with the only bi character. I can understand why some feel it can be considering kind of cheap and convenient to eventually pair those two up, hence its contrived nature.
And then you add in the "not feeling it" part. You know, the mutual chemistry. It has been very evident in almost all the other relationships and how they were built up that it made a lot of sense in there was some believable build up and chemistry boiling between characters. Then you have the latest where Dora really seems to have no clue of her feelings toward Tai (and she admitted she could tell Tai is very infatuated with her). Note she didn't say she was infatuated with Tai. Isn't that one of the first steps? You become a bit infatuated with the person you want to date / after a 1st date?
From the spacey Dora during the date to this revelation, it has gotten even less convincing of a pairing.
That's what I think some people mean by contrived. I personally think it would have been a bit more believable if you introduce a new girl that Dora just meets on her own and really digs her off the bat and tries a date than mackin' all of a sudden on Tai.
But, it is what it is. Some people see it differently, some see it the same, others see an in between analysis.
I agree on the arc getting a little over drawn and a bit dull.....I blame that on Hanners missing from the strip for far too long.
And Marigold! Where's Marigold!?
Ow, I've been in a similar situation to Dora's. Thirteen years ago, I was on summer break at Belle-Île. I met a girl at a fest noz (a kind of traditional-ish festival) and we hit it off pretty well... Except I didn't feel really in love. I liked her, a lot, she was fun, smart, attractive. But I wasn't in love and my lukewarm feelings puzzled even myself. I supposed that somehow I wasn't in the proper state of mind to fall in love. And we didn't have much time to try to let my feelings build up. If we had been on the same page, I'd eagerly have considered friendly sex with her. But she was in love with me, the asymmetry of feelings was too great.
I think this will be a cause of conflict. Tai is still trying to change, but sex=success will still be in the back of her mind. I hope/think Dora will really be trying to put off the sexy time with Tai unless she's sure she's committed and really wants to pursue a real relationship with Tai. That could cause friction with Tai who may be put off by Dora not taking Tai's advances or initiating them.
And honestly, when you have someone that has a 15 on the 1-10 scale of interest in you, but you're still questioning what your's is (likely a 2-3)....I don't really consider it fair to the other person. The noticeable lack of equal levels of sexual and romantic interest is just astonishing.