I have good news and bad news. The good news is Final Fantasy VI, otherwise known as the best Final Fantasy, is now available on Steam. The bad news is it's a port of the hideous mobile version.
As for while the mobile versions of classic Final Fantasy games look so terrible, developers Bill Stiernberg (Cosmic Star Heroine) and Lars Doucet (Defender’s Quest) have explored this subject in great detail, mostly finding fault with inconsistent art that renders the whole thing a clashy mess.
You can find nicer-looking iterations on PlayStation Network and Nintendo's Virtual Console, but if you're dead set on playing this on PC (and you're anti-emulation), this is option that exists.