They didn't officially announce a maint mode, they said this year was going to be light on content. Don't know whats beyond that and I am almost sure this won't be the last thing they add. Content means just that, things to do. Plenty of things had almost 0 to do with the story and were just things to keep people playing.
You are actually very easy to please
Don't assume
This is 100% a looking from the outside in sort of thing as someone that plays XI on and off but only since ~2019-2020 or so and also plays newer, more raiding focused MMOs as a raider. Something like a Mythic raid in WoW or an Ultimate raid in XIV are celebrated content pieces as the hardest-of-hard stuff, which from what I can gather is the same sort of concept as a Master Trial. And yet that style of content doesn't seem all that hyped or celebrated when it happens here. Is it a community desire for only power-related rewards and not prestige cosmetics? Distaste about recycled content? Are Master Trials not well designed for XI's combat system and are instead just sort of gimmicky once the specific gimmick has been figured out and not actually fun to play (I've never done one, only read some guides and seen some clear VoDs)?
I'm asking this in good faith and out of some genuine curiosity by the way, not as some sort of gotcha.
I think people have just become really pessimistic for anything added to this game since the end of ROV. Right now, its almost justifiable given the neglect, but the general sentiment has been like that around the forums for a long time. MTs were fun and challenging when they were new and most people I've talked to that have done them have enjoyed them. The reward is a cosmetic item/bragging rights which is fine, its just padding mostly.
As far as the power creep situation, I don't think its that bad as you say. There are still some challenging fights despite all the power we've gotten. A lot of them have the luck element but in general they seem to always come up with ways to keep people engaged with the battle system. Most people thought the same thing when we were at the end of Abyssea, until Voidwatch came and turned everything on its head.
Odyssey gear was the worst gear/progression choices they have done in a while but I'm sure they can come up with something if they were to create other content down the line. I thought the gimmick for Odyssey was interesting, even though most hated it. Giving some kind of handy cap has been something they've done for a lot of content to keep it interesting. At absolute worst they could go back and cut down the numbers on everything like they did with XIV not long ago lol.