I apologize for the ensuing wall of text. I'm on my phone and posting is a pain in the ass, so I'm trying to get everything at once haha.
I don't know anything about tag since it wasn't available in the build I played. Outside of Tina, the only characters I can play well are Helena, Leon, and a little Bayman, so I've never really messed around with Lee too much. He's a very powerful character, so I'm sure he could work well with anybody. You should mess around with them and see what you find! Personally, my teams are going to be Tina/Helena and Tina/Bayman since I know she works well with both of them already.
As for how Tina stacks up competitively, I personally feel like she'll end up being mid tier, maybe high mid at best. She's good, but there are other charcters who are just better imo. Sarah, Akira, Eliot, Jan Lee, Bayman, Christie, Busa, Kasumi, and maybe Leifang and Kokoro all just seem to be a bit better. Tina's main problem to me is that she's pretty predictable, slow, and I feel like a fair amount of her moves lack priority are easy to hold on reaction. That being said, she has sit down stuns, guard breaks, lots of safe moves, ways to guarantee damage, good offensive holds, and nasty damage output. She's viable and has good tools, but I don't think she's as strong as other people have been making her out to be.
I feel like I should stress that this is just one guy's opinion that was formulated after only one weekend of play in an unfinished build at a pre-release tournament. When the game actually launches and more tech is discovered, we'll develop a better idea of how good or bad she actually is. That's why I feel it's a bit silly to talk tiers at this point, but you asked haha. Also, I love these kinds of discussions.
And synce, I can't really compare them since I didn't even touch Bass. I wanted to, but the casual rotations were pretty long and I mainly wanted to focus on Teener. If I had to guess, I feel like Bass' mixup and guard break games are better than Tina's, but she has the edge in speed. I want to say her sidestep game is better than his, but I don't know for sure.