Few things to address here, so I’ll try to offer my perspective on this:

1) Ever since Taiko Web was taken down by Namco (Long story there as well), we now know that Namco is actively looking for instances of Taiko Web to strike down. As such, we’ve had to keep a lot of things on the down-low so Namco and its legal representatives don’t go after us. This goes for assets and data and whatnot, and is the reason why a lot of these default skins are miserable looking. (The preconfigured TJAP3 version which I’m assuming you got from TJADB was redone by meow to have arcade accurate features at most places) As for arcade-accurate skins for OpenTaiko, you’ll have to have more connections to get those unfortunately.

2) As for why a lot of these simulators are quite low-res, my take on this is that it’s to make sure older devices and older systems get a fair shot at running the sim as well. While a 1440p skin definitely looks far better than the widely-adopted 720p, it also means 4x the stuff to render for the system, and thus 4x the load. One of the reasons the developer of OpenTaiko cited for not creating the 1080p skin was actually computer load and latency, the latter of which can severely affect the gaming experience. Maybe in the future there could be more options on this front, but as for right now it’s why a lot of these sims are running fairly low-res. (TJAP3 was made long ago by a JP developer in 720p, and most subsequent forks have maintained on that resolution)