Things like this are difficult to judge. You can't really compare most Jedi in the 1000 years or so BBY to anyone outside of that time period and vice versa. For 1000 years, Jedi didn't really get to test their skills against other saber users in serious combat.
We can say that Yoda and Windu were skilled swordsmen because of their duels with Sidious, who was known to be a skilled swordsmen, and would have had to prove himself in combat to his master to avoid being cast aside for another apprentice.
This is similar to what's pointed out about the lost tribe in FotJ. They haven't tested themselves in true combat for a millenia, so the skywalkers just cut through them like butter because they're battle tested.
Darth Bane was a skilled swordsman, but his most obvious display of skill in dueling multiple jedi masters at once deserves an asterisk, because he was virtually invulnerable to saber damage at the time. Also, his sith contemporaries at the time had dwindled in skill relative to sith of times past because of the need for troops in the battle with Hoth's Army of Light.
Luke Skywalker proved himself in battle countless times against some difficult opponents, which his father never really did.
For pure saber skill, I think any top 5 list should consider including Sidious, Caedus, Luke Skywalker, Yoda, and Mace Windu.
Keep in mind, to truly be good, you have to be tested. And the strength of your fallen opponents is the best metric for determining how good of a swordsman you are yourself.
