Sephiroth - Uh HELL NO! Even with the Compilation in mind, it's pretty fucking hard to actually feel any sympathy for Sephiroth when his reaction to finding out all the truths about him, is to turn his anger against EVERYONE instead of just the people who created and used him. The funny thing is during the intro of the video he shows a clip of Kefka when discussing villains who are "irredeemable", despite the fact Kefka is evil for very similar reasons to Sephiroth. Neither one is sympathetic because their own actions are irredeemable, REGARDLESS of the circumstances which led to them.
Seymour - I'll grant you that the actions he takes actually make some semblance of sense, given what he went through and the nature of the world, but this doesn't make him sympathetic or someone you'd feel sorry for. Ultimately he's still a power hungry mad man who murders people while taunting and laughing about it to another of their race, all while advocating for EVERYONE dying as a release because the world is so shit. There's a reason why Anima says "My Son, do you NOT hate him?" while even Yuna herself is pissed off with him.
Seifer - Okay this one I'll grant you even though him failing the SEED exam is absolutely his own fault, unlike whatever it was you were implying there.
Ardyn - NOPE! Dude literally had the option to screw over Bahamut by just doing NOTHING, but instead decided to do exactly what he wanted while somehow pretending that he was being defiant? About the only thing you can maybe say is understandable is him killing the Gods, everything else he does is still irredeemable and it's pretty hard to feel sorry for him at that point.
Caius - This one I don't think anyone would disagree with.
Golbez - Okay this one's fine too.
Emmet Selke - Don't know how sympathetic he is or isn't.
So yeah pretty fucking shit video overall, with almost half the list lacking any kind of sympathetic traits that would allow one to feel sorry for them, while also excluding more obvious options such as Shuyin from Final Fantasy X-2. Like how the hell do you make a list of FF villains you feel sorry for and include Seymour OVER Shuyin?
He seems to be under the mistaken belief that simply HAVING a tragic backstory is enough to make a villain sympathetic but that's not how that works. Ultimately they are still responsible for their own actions and if those actions aren't really justified by their backstory then they are not sympathetic.
Speaking of Caius isn't he also one of the few villains to actually achieve what he wanted?