Ragnos was incredibly powerful, but battles between Sith and Sith or even Jedi and Sith must ultimately come down to lightsaber combat. and in that, Ragnos would find himself hard pressed to win. Tulak's abilities were revered in a time of lightsaber duellists who make Revan and even Exar Kun look like children.
Knew who? Hord? She knew of him. Much more than did the Sith of Korriban in Malak's day. She was a better judge of his abilities than say, any one of us. She knew of Revan's potential, and she still cited Tulak Hord as being legendary in his time, a time when lightsaber duelling was perhaps at its zenith. We can only imagine the fantastic battles that took place at that time and he was the best, undisputed. He was most likely slain by treachery, but he did warrant a ceremonial burial chamber in Korriban next to greats like Naga Sadow, Marka Ragnos, and Ajunta Pall.
Oh i'm not disputing his greatness, I really do think he could kick pretty much everybody into oblivion no matter who his opponent. But to say that Revan and Exar Kun would be like fighting children is a bit overboard if you ask me...
Still i wouldn't doubt for a second that he would win from them, but not as easily as you would win a fight from a weak 12 year old
Marka also came from the time of great lightsaber duelists and he did live for centuries. With the Force I think Marka would win.
I must agree with Fishy on the children issue. Kreia referred to Jedi in general. Revan was far past the average Jedi even when Kreia was his master. Then he entered the Mandalorian Wars, learned everything about the Sith, fought the Republic, was the Dark Lord for 2 years, came back even stronger, plundered many Sith tombs and artifacts on Korriban (getting Tulak's tablet), and then recovered his memories of Malachor and the Jedi knowledge. So Kreia didnt really know how powerful Revan was, nor was she even comparing old Sith Lords to him. Besides, Kreia's information is probably accurate but she is talking about something from 1,000 years ago. I dont think Tulak, Marka and the others were necessarily the most powerful beings ever.