Just wanted to agree with what was said above and add a few points.
Firstly, no warning about this which makes it even worse because otherwise we could've had a chance to give our thoughts on it before it hit.
Secondly, no other prize fights require your fight team to match the mods. Can you imagine people competing for Fukua in the PF having to USE a fukua in their offense team!? Most of the Fukua people slapped on their teams were silvers and barely invested in (I'm not bashing anyone for it, I'm part of that club too). And this would give a SERIOUSLY unfair advantage to RNG lucky players who happened to get a diamond fukua and make their defense team a living nightmare.
So let's take that logic and apply it here.
I have one decent water character. Just one. And it's not even from relics (I'm just that unlucky). For the first 20ish fights I'll probably be fine without it, but then as they get more difficult I'll really start to have a hard time using the same character on my team over and over. She's useful, she's invested in, but she just can't main carry me later into the streaks. And I'm someone who can consistently reach top 10% if I wasn't so lazy with elemental pfs. So what about the earlier game players? Isn't needing a decent elemental fighter to participate asking enough of these poor folks? I mean, they're getting bashed from every angle here. They probably have about 3ish good fighters? Enough to get them somewhere in a prize fight but not enough to choose from.
AND the icing on the cake are deployments which ask for certain fighter of certain elements. That also serves as an incentive for players to invest in those fighters BUT they can't do both PFs and Deployments because deployment fighters can't be used for offensive teams while they're away but CAN BE USED FOR DEFENSE TEAMS.
Final point. Elemental PFs are a great place to level up bronze foddler since you can't in character PFs. So now you're more limited in what you can level up when.
So let's recap a bit. Most players think this is a terrible mod, even later game players who have great collections and enough fighter to make this worthwhile. I understand the themed defense mods, but themed offense teams is very poorly received. It gives unfair advantage to those who have lucky pulls, and those players get enough advantages as is, and really hurts incoming and midgame players even more than the rest of this update already has. Please reconsider this change.