You can't disagree with facts. Xanesh was not target dummy. Going with your logic every boss is target dummy if you die at the beginning and let other people carry you.
Aside from her complex mechanics she didn't have other complex mechanics.
Lets go:
Blackhand - one of the worst bosses in that raid. Boring, clustefuck, main mechanic was tank kiting that demolisher or whatever it was called.
Operator was good fight, not better than Xanesh but good.
Gul'dan - was ok, too long, a bit too complex but overall not even close to xanesh.
Argus - terrible fight, boring slog, too long, boring mechanics, puggable first week. Far from xanesh.
Kin'Goroth - it was ok, balls were good but that was practically the only mechanic there, laser was bugged.
Mekkatorque - pretty good, it could have been considered on par with xanesh if not for random bugged slams and random balls falling to wrong people wiping raid.
Jaina - too long, it was good but far too long.
Funny thing is you didnt list hanzgar & franzok and oregorger that were both leagues above any other bosses in BRF.
Nope. Not even close to Xanesh. And no, there isn't a single boss in entire wow history that is "leagues above" xanesh.