The first Xenoblade game is the only actually good one, I love X but it's story is whatever. 2 and 3 are not real games, they are genuinely abysmal in storytelling, writing and characters. I'm sorry, someone had to say it.
If you really only want to play X and if you have a decent PC, you can emulate X on Cemu with mods that'll make it look even better than the definitive edition I would imagine. That's how I played it and even without mods I'd say it graphically holds up honestly.
With that being said, no console is worth buying for 1 game, and with the Switch 2 on the horizon I don't think buying a Switch unless it's a used one for cheap is worth it at all. Take it from someone who owns one, the console lacks so many quality of life features that other consoles have and it's services are so slow and unreliable that I wouldn't buy one unless it was cheap.