The problem is that you have to base their power on what we know. Are we arguing for Ragnos or for the Ancient Sith here, Darth Sexy? It does sound like you're suggesting that every Ancient Sith > every modern Sith, which is not the case. Palpatine, Kun, Bane, Revan, Dooku, and even Maul would likely wipe their ass with the majority of the Ancient Sith because the Ancient Sith haven't exhibited anything that suggests that they are on par with them.
Now, if you're talking about the upper echelons of the Ancient Sith, you have another case. I'd count Ragnos among the very most powerful, but the other Ancient Sith? Rofl. Hell no. The only thing that we can safely argue for the Ancient Sith is that they were the originators of the vast majority of the modern Sith's knowledge base. But knowledge != power.