In the Sword and Exquisiteness (Ming Jian Feng Liu), there are some pretty extraordinary displays of martial arts. Though I don't have any evidence of it, I would imagine the leaders of the 13 sects to be somewhere around a Quan Zhen priest level. From the few times they fight, and their fame and status as leaders of sects, I don't think they should be ranked any lower. If anything, they seem more impressive than the QZ priests, but I'll just use the lower side for comparison's sake.
In LOCH/ROCH, we see that Huang Yaoshi cannot subdue a Qiu Chuji or Ma Yu in just one stance, yet in SaE we see that there are THIRD tier fighters that can subdue people of the 13 sect leader caliber in one move! These are not surprise moves either, no trickery is involved -- they just plain kill or show the ability to kill them in one move.
The sick thing is...I'm not even done reading it yet. The famous Mr. Dongguo has not shown his face yet, and we already see people that in all theory should be 2 tiers above the Greats of ROCH/LOCH. I somehow don't think Sweeper should be ranked #1 anymore.