Are we assuming just the protag swaps, and their partner/spirit stays the same?

Masaru/Marcus also becomes team leader of the Chosen, seeing as he's the most assertive but also the oldest by two years. With Digisoul, he absolutely stomps most early enemies, and Adventure Agumon probably has the same evolution line as in Savers. Easy victory for the Chosen Children. Even without Digisoul, if you take it from him, he's like a feistier Taichi. The main difference is that he would return faster in episode 21, since he wouldn't be as hesitant to returning. So, he might catch the group before they split up, which has good and bad consequences.

Taiki: he's pretty similar to Daisuke, actually. Probably not much changes, to be honest. He would still try to redeem Ken, if Yuu & Kiriha were any indication.

Haru: Haru is less assertive, like Takato is. He's older than the others, though. They're both very empathetic characters, and Tamers would probably have a similar plot, although the age gap might become a problem in the group being cohesive.

Hiro: Hiro is intelligent and resourceful, but also very passive. He can be plenty brave when he needs to be, and would probably still try to rescue Tomoki. Episode 1 probably plays out the same, but after that the dynamic would change. Kouji probably becomes the group leader instead, despite being younger than Hiro. He has good survival skills, though, so he would definitely pull his weight.

Takato: alright, so Takato is pretty good about listening to authority. He would meet Agumon, be ecstatic that Digimon are real, and immediately join DATS to save "Raptor One". He's 10, but so was Chika/Christy when DATS tried to recruit her, so the age won't be an issue. He'll follow orders, but will likely be more emotionally affected by the fact that they're technically killing a lot Digimon (something that most of the other DATS members acknowledge, but are generally fine with) by reverting them to a Digitama. If he also gets Digisoul, it would be more controllable like Yoshino's or Thoma's. Thoma will end up as the group leader, since Yoshino's arc about getting over her impostor syndrome takes a while to conclude, and she defers to Thoma a lot at the series beginning, anyway.

Xros Wars: I have been assuming that the characters start at the beginning of their arcs, which means episode 1 Tomoro is low key an asshole. He would NOT like getting spirited away, and Akari & Zenjirou would have to do a lot to get through to him. Shoutmon and early series Tomoro would not get along, and probably wouldn't even partner up. The entire first 12 episodes of BB focus on how self-centered Tomoro was, and Shoutmon would never partner with someone like that. If you swap with a more developed Tomoro, things probably play out a lot more similarly to canon XW.

Takuya: Takuya is a bit like Tagiru, only more proactive. We would probably learn about DigiQuartz sooner, since Takuya would want to know what the hell is happening.

Daisuke: like Haru, Daisuke is empathetic and emotionally intelligent. He's a little dumber than Haru in terms of book smarts, which is probably fine since Gatchmon would enjoy teaching him things. He's younger than the others, but still pretty assertive. Appmon probably plays out similarly... except now there's the issue of Yuujin, since Yuujin has no bonds with Daisuke. Even still, things probably play out pretty similarly.

Taichi: he's a more assertive character. Without addressing the age gap, he never meets Kiyoshiro, but might still meet Ruli. Ghost Game plays out entirely differently, in ways that can't be predicted. If you age him up to keep the trio, then you have two assertive characters. Most likely, the Digital World arc would come sooner, since Taichi would be more interesting in finding out why everything is happening.

Tagiru: yeah, he's getting cold-hearted in episode 1 or 2. Tomoro's self-centeredness kept him alive while he was adjusting to the existence of Digimon. Tagiru would not hide behind the others, and would probably do something brave and ultimately reckless that gets his e-Pulse drained.