Puyo Puyo Tetris was the only game I ever bought a non-North-American version of, after watching Giant Bomb play it. As far as I can tell, it never got a real NA version for Xbox, or if it did, I missed it. I didn't even notice the Steam version of PPT1 until looking it up for this comment. The slowdown problems you experienced may be relegated to the Switch version, because...it's the Switch.
"...any developer releasing a multiplayer game in this day and age without cross play is making a huge mistake." They're the ones who have to pay for it though. You're talking about a game that you acknowledge as niche, which is even harder to justify additional expenses for. The only entity offering cross play services for free is Epic, and some people, for reasons I don't understand, will whine about Epic Online Services if the game includes them. Otherwise, it's an expense out of the developer's/publisher's pocket, and in a world without LAN and direct IP connections, that means the online dies when that expense no longer makes financial sense. You may not like playing against bots, but you'd also hate playing against absolutely no one. They're not the first ones to pull this strategy, and there's a lot of nuance to it.
As for appeal to bring new players in, I was at Combo Breaker 2022, with a friend of mine. He was watching DBFZ top 24 (IIRC) right next door, and he couldn't stand the sounds coming from the PuyoPuyo stage, so I'd call that a barrier to getting new players in, too. I don't know that some new game is going to solve the player acquisition problem without a new gimmick. My recommendation? Make your own PuyoPuyo, like Kirby's Avalanche, but with blackjack and hookers.
The slowdown problems you experienced may be relegated to the Switch version, because...it's the Switch.
It's a 2D puzzle game. It's not doing anything the Switch shouldn't be able to handle. Champions never had any problems. Even the Wii was perfectly capable of running 20th, and not much has actually changed since then.
Like, I know the Switch is not the beefiest system ever, but this is not a game that should need a PS5 Pro or whatever.
You may not like playing against bots, but you'd also hate playing against absolutely no one.
That's the current state of every platform but Switch.
I'm well aware that crossplay isn't trivial, but it's too important to not be a priority. If you're making a multiplayer game and you want it to have a playerbase, crossplay is vital to keep your game alive. A publisher the size of Sega has the resources to get it done.
I don't know that some new game is going to solve the player acquisition problem without a new gimmick.
Does simply being content-complete count as a gimmick? It's something we still haven't seen yet in the west. I think 20th and Chronicle had a ton of great things to offer new players. Chronicle's JRPG story mode might be the most innovative onboarding experience any puzzle game has ever seen.
Too bad the west never saw it.
The Switch should be able to handle it unless the game was coded in some toolset where performance wasn't a priority, because it's only Puyo Puyo. Then suddenly it's on a low spec platform where performance matters.
And it's not that cross play is non trivial; it's that it's an ongoing expense in most cases. To justify an ongoing expense, you're going to need ongoing revenue, which Puyo Puyo probably isn't going to bring in.
missingno@fedia.io to 
Puyo Puyo Tetris was the only game I ever bought a non-North-American version of, after watching Giant Bomb play it. As far as I can tell, it never got a real NA version for Xbox, or if it did, I missed it. I didn't even notice the Steam version of PPT1 until looking it up for this comment. The slowdown problems you experienced may be relegated to the Switch version, because...it's the Switch.
"...any developer releasing a multiplayer game in this day and age without cross play is making a huge mistake." They're the ones who have to pay for it though. You're talking about a game that you acknowledge as niche, which is even harder to justify additional expenses for. The only entity offering cross play services for free is Epic, and some people, for reasons I don't understand, will whine about Epic Online Services if the game includes them. Otherwise, it's an expense out of the developer's/publisher's pocket, and in a world without LAN and direct IP connections, that means the online dies when that expense no longer makes financial sense. You may not like playing against bots, but you'd also hate playing against absolutely no one. They're not the first ones to pull this strategy, and there's a lot of nuance to it.
As for appeal to bring new players in, I was at Combo Breaker 2022, with a friend of mine. He was watching DBFZ top 24 (IIRC) right next door, and he couldn't stand the sounds coming from the PuyoPuyo stage, so I'd call that a barrier to getting new players in, too. I don't know that some new game is going to solve the player acquisition problem without a new gimmick. My recommendation? Make your own PuyoPuyo, like Kirby's Avalanche, but with blackjack and hookers.
It's a 2D puzzle game. It's not doing anything the Switch shouldn't be able to handle. Champions never had any problems. Even the Wii was perfectly capable of running 20th, and not much has actually changed since then.
Like, I know the Switch is not the beefiest system ever, but this is not a game that should need a PS5 Pro or whatever.
That's the current state of every platform but Switch.
I'm well aware that crossplay isn't trivial, but it's too important to not be a priority. If you're making a multiplayer game and you want it to have a playerbase, crossplay is vital to keep your game alive. A publisher the size of Sega has the resources to get it done.
Does simply being content-complete count as a gimmick? It's something we still haven't seen yet in the west. I think 20th and Chronicle had a ton of great things to offer new players. Chronicle's JRPG story mode might be the most innovative onboarding experience any puzzle game has ever seen.
Too bad the west never saw it.
The Switch should be able to handle it unless the game was coded in some toolset where performance wasn't a priority, because it's only Puyo Puyo. Then suddenly it's on a low spec platform where performance matters.
And it's not that cross play is non trivial; it's that it's an ongoing expense in most cases. To justify an ongoing expense, you're going to need ongoing revenue, which Puyo Puyo probably isn't going to bring in.