You're right, I'm misremembering. They took out the long timelines of events from more recent books, but The Beast was mentioned in 6th edition (Path Walker linked the Lexicanum article for us here).
The Beast is described as having nearly taken over the galaxy, which is pretty damn impressive. Ol' Ghazzie certainly has a kunnin' plan, but he hasn't quite reached that level yet. The Beast was more badass than the Ullanor warboss, and that one nearly killed the Emperor and his favorite neglected son. The Beast is several shades 'arder than Ghazzie, but Ghazzie's alive and therefore has room to grow.
No true son of Gork will deny that Ghazzie is ded 'ard, killy, and kunnin'. He's definitely the biggest, baddest, and smartest Ork in the galaxy currently at large. He's probably reached Ullanor-levels of dangerous with his Armageddon campaigns. But The Beast nearly conquered the entire galaxy, while Ghazzie has conquered a couple systems. He has a ways to go before he reaches Beast-level. And if the fluff ever moves forward, maybe we'll see it. He's just not there yet, though.
We also have to remember that the recent fluff and rulebooks have all been looking at "current era" 40k. Really, most of the fluff and rulebooks have been "current era". Ghazzie looks like such a badass because they focus on him more than the older warbosses. Compare the Lexicanum page for [URL="http://wh40k.lexicanum.com/wiki/Urlakk_Urg"]Urlakk Urg[/URL] (that'd be the Ullanor Warboss) to more modern warbosses like [URL="http://wh40k.lexicanum.com/wiki/Snagrod"]The Arch-Arsonist of Caledon[/URL], [URL="http://wh40k.lexicanum.com/wiki/Nazdreg_Ug_Urdgrub"]Nazdreg[/URL], or [URL="http://wh40k.lexicanum.com/wiki/Ghazghkull_Mag_Uruk_Thraka"]Ghazzie[/URL]. We know a lot more about each of them than any of the "legacy" warbosses on whose shoulders they stand.
I feel ya on this one. I think I read one short story where an Ork Kommando mob ambushed some stupid 'oomies, written from their perspective, but all the rest have them as mostly personality-less hordes of redshirts to be mowed down by the heroic Beekies. Still, I'm pretty interested in getting more information on The Beast, since he should be such a big figure, and all we currently have is one tiny paragraph proclaiming him the biggest, baddest boss to ever stomp a grot.
Also, Ghazzie's just been less fun ever since GW killed off Makari. It's nice that The Lukky Stikk gives him a nod, but still, a shame.