Darth_Plagueis, have you even seen the movies? 🙂
You say that thousands of Jedi's died, but only two sith right? First off, how many of those Jedi's died by a lightsaber in a fair fight? You of course can't count the order 66 deaths, because Sith or Jedi would have died under the same conditions so those are mute. You also can't count Windu or Palps eventual death, because they were both blindsided. So that leaves what?
Maul, Dooku, Anakin, Vader, and Palps on the Sith team.
Qui gon, Obi wan, Yoda, Windu, and the three tools that went with windu to arrest palps for the Jedi team.
So of all those siths, Maul and dooku actually die by a Jedi's hand. Vader and dark side anakin get beat by a Jedi's hand. So basically 4 loses.
Of all the Jedi's, Qui gon and the three useless pieces of crap get killed by a Sith Lord. I shouldn't, because they were too young, but just to help out your argument, we can also say that AOTC obi wan and Anakin lose to Dooku. So that would be 6 loses for the Jedi's, even though only Qui gons was considered a straight up loss. Two young jedi's lost to a very old and strong Sith, and three useless Jedi's lost to a Sith Lord. Big deal.
From my count, it's basically even. Jedi's and Siths have proven that when they get that strong, they are EQUAL in power. Yoda, Obi wan, Windu, Palps, Anakin, Qui gon, Maul, Dooku, they are all very powerful. I certainly can't see your argument for saying the dark side is stronger.
The only reason it appears that way, is because there are only two siths at any one time. And they have never fought anytime out of their absolute peak. The Jedi's however have been shown to fight as padawans and young Jedi Knights and still do ok. By the time they are at full potential, they start to beat the Siths. Light and dark are equal...