VI's saving grace for me is that it actually has one of the most relevant plots in the overall Ys 'lore', but as a game it's... very rough. Sure, you gotta respect it for basically introducing the gameplay style that gave us Felghana and Origin, but both of those games refined the experience tenfold. Playing VI nowadays is sort of painful, and the whole gimmick with the swords wasn't very fun, ESPECIALLY when it was used for platforming which was just a nightmare overall on that game.
That said, even though I do think the plot is nice, the actual bosses and stuff are also some of the most forgettable. The final boss in particular is like, a decent concept, but it looks so damn lame, and the battle itself is just terrible. Add to it the fact I find VI's soundtrack to be like the worst one in the series (aside from V's, but V simply doesn't have Ys music, it's... something else) and yeah, not a fan.
I do agree that V is bad though, it's just V is the same old V from the SNES era. Whenever Falcom gets around to remaking it, I think there's a fair chance I'll end up preferring it over VI. Although I'll tell you this -- I don't think V is a bad game in general, it's just a bad Ys game. It doesn't play awfully nor is it awful in any of the things it tries to do, it just commits the sin of not really having anything that made Ys famous. Could be named anything else and no one would notice, lol.