Shinji being talked into staying in part by TJ was really sweet and a good, heartfelt moment. I think that Shinji almost leaving, contrary to what people might expect, actually has increased his chance of winning a lot. He just had his arc. Much earlier in the show, I recall him talking about being lazy, being bad at school, and giving up on things. The language barrier means it's harder to get a good sense of his personality, but it sounds like losing steam and lacking perseverance is something he has struggled with. This moment also cements TJ as the hero of the tank, and Tay as the villain. It will make an interesting and satisfying final 3 to watch compete, now that TJ and Shinji are teamed up.
I personally still want Tay to win, but I have to admit she makes a good tank villain, better than I expected her to. At this point, any one of them winning would feel satisfying, which is a good place for the show to be in because there's no "bad" ending. Without Shinji's struggle tonight, him winning would have been the bad ending, because it would have been boring and felt unearned.
Edit: In season 1, the final two did not have any unique dynamics between them. Letty and Josie mostly had left each other alone up until that point in the tank. I thought the Season 1 finale was very good, but there was unfortunately no personal tension between the two fish. I think that in this case, the emotional stakes will be higher, and that is a good thing. It may not be the most dramatic or entertaining finale (imagine Jimmy vs Tay or Jimmy vs TJ) but I predict it will be a good one. And the danger of a "Jimmy vs" ending is that the ending sucks if Jimmy wins, so it has to be rigged so he loses. In this case, they shouldn't, and hopefully don't, try to rig it, because it truly could go any way and still work with these 3 fish.