First of all he's not going to beat 10.000, he's going to defeat a few that are in working order a lot of the others are down for the count by the time Ragnos reaches them. The weapons of the droids will take out a lot of Jedi.
Now they aren't all going to be in the same room at the same time, no they won't be meditating but they won't all be able to attack at the same time. And imagine the huge downfall in moral if you see the leaders of the order who would no doubt fight first die with a single blow. Thats all it would take to defeat Yoda or Mace or Obi Wan Kenobi or well anybody else in the council. Ragnos would slaughter them the rest of the Jedi will be scared confused afraid. Now in front of them is the biggest threat they have ever seen and none of them stand a chance they are going to be scared they ar going to lose focus perhaps get angry or perhaps just confused, that in combination with a bunch of very powerful droids shooting at them... Well its going to hurt. The Jedi will die...
No Ragnos isn't more powerful then 10.000 Jedi combined, but the Jedi can't combine their powers they can't work together and they are going to be scared tired and alone... Ragnos will have no trouble cutting through the few that reach him while the droids kill or keep the rest away.