That is an odd one. I think it's a hold over from 5E, honestly. Big numbers good and all that. They seemingly wanted to resolve hit point bloat, which they did. Trouble is they mostly shifted that bloat from HP to thresholds. I'm the same as you on this one. I'd much rather they skipped the separate damage roll for big numbers and went straight to dealing HP. Like success with fear, 1 HP; success with hope, 2 HP; critical, 3 HP. Or something. The whole damage roll vs thresholds thing, including the weapons and armor thresholds subsystems, just seem like a pointless extra step. Well, maybe not pointless. A lot of people really like chucking a lot of dice and saying how much massive damage they did.
Yeah. Thresholds again. Say they're 8/16. If you deal 1-7 damage, that's 1 HP. 8-15 damage, that's 2 hp. And if you deal 16-infinite damage, that's 3 HP. There's an optional rule to deal 4 HP if you double the highest threshold, but the point still stands. Tag teams makes it more likely you'll deal 3 HP rather than 1 or 2 each...but you lose out on the possibility that you could each deal 2-3.