This argument about Tama's fight against a blackbeard captain is just nonsensical. Why? Because is all based on fan speculation.
She could help in Chopper's fight with Doctor Q, She could have a giant Kaiju fight with Sanjuan Wolf, it could turn out the 10th captain is a perfect match for her or has a similar ability. We don't actually know.
Remember when the entire community believed Shiryu would get Jozu's fruit? Trying to predict Oda hundreds of chapters in advance while powerscalling an un-named character holds absolute no weight, it's all just blind speculation.
Just like Yamato's character arc and emotional payoff is just fan speculation at this point.
Tama has bonded with the crew throughout Wano, way more than Yamato or Carrot ever did, and that's a fact you can't deny.
It's something I can actually point out in the manga and say that, in her first two chapters, Tama formed a deeper bond with Luffy than Carrot did in 80 chapters, and that's before Luffy fed Tama or Tama started seeing Luffy as the second coming of Ace. Meanwhile, Yamato seems to be the one who's been getting Carrot-like moments with the crew. (hugging/ biting luffy and experiencing the world for the first time). Luffy still doesn't know Yamato's name 70 chapters after he met her, while he started calling Tama by hers in the chapter she was introduced. These are also facts you cannot deny.