If you care about image quality, definitely get the PC version. The Switch version is a great port and looks great in handheld mode or a smaller TV/monitor, but anything bigger and it is quite blurry. There's other graphical improvements on PC beyond the resolution increase such as a much further draw distance which can be changed to be even further with a simple .ini change and, as you mentioned, higher framerate. As nice as the additions to Switch are the original DQXI isn't suddenly bad because it doesn't have that additional content. I personally can't put the additions over the increased image quality of the PC version at a higher resolution, max settings, and the expanded draw distance with the .ini mod. It helps that the biggest addition to the Switch version, the Orchestrated Soundtrack, exists for the PC version as a mod.
It looked really really bad on my 55". Cutscenes were okay, but turn the camera towards the main character's face during gameplay and it's a jagged/blurry mess. NPCs also became super blurry if you walk more than 5 feet away from them, but yeah it was fine on handheld mode.
I would've gotten it for Switch if I was planning on playing on the go most of the time.