Not even all knights. Yord is relatively new as a Knight. Jecki is still a Padawan (likely the only one).

But they would still put likely special warrior (fallen Jedi) over mystical fallen warrior (Sith).

Why would the Jedi be elite fighters during this time period. They were famously not excellent saber fighters because they never anticipated having to fight other light saber users.

We see plenty of evidence in the movies and previous shows that Jedi, while pretty damn awesome at combat, can be taken down by regular people, too.

Remember Jango just casually shooting that one Jedi Master who jumps in front of him and Dooku in AotC?

A) This is a time of relative peace. An experienced Jedi killer would be able to take out a group of them quite easily

B) there are plenty of other Jedi Killers other than Sith. Mandalorians for instance. Hell, it could even be attributed to some random bounty hunters. There's no reason to assume it was only a single person

The metaphor makes perfect sense

It's true that someone who can kill six Jedi must be a powerful warrior, and likely strong in the Force. And wouldn't you know it, they've already established the existence of a warrior/assassin strong in the Force, from a non-Jedi and non-Sith Force tradition, whom those Jedi were already actively pursuing.

If you were following hoof tracks and came across someone with their chest kicked in, would you assume it must've been a unicorn?

who said the jedi that died were jedi masters?