You're missing my points, Jaffar.
I already play Ultramarines, and I like them. They're nothing like Orks, and I certainly am not looking to switch to a horde army.
My point was that the Ultramarines had the biggest legion by a lot, and that basically made them the most powerful legion. Not because they did swarm the battlefield with massive numbers, but that, in some theoretical matchup against some other Legion, they could, and it would basically be the end for the other Legion.
I want elite guys, and Ultramarines, like any other marines, certainly are that. I just think that they have plenty of cool fluff, a cool and admirable Primarch, and the fact that they have always been considered to have been the largest and best organized (and thus, most powerful) Legion certainly supports me in both of those points.
In point of fact, Ultramarines tended not to use their numbers to swarm individual battlefields with guys, but rather to cover more space--during the Heresy, IIRC, Guilliman sent countless guys all over the place to make sure that there would be military power and symbols of Imperial might in as many parts of the Empire, no matter how remote, as possible. It was his effort to prevent the Heresy from bringing the Empire down in a storm of chaos and doubt--and, by all accounts, he was pretty successful. It isn't too much of a stretch to presume that without Guilliman, the Empire would be a mere fraction of the size that it currently is, having lost billions of outlying worlds to the internal turmoil that the
Heresy generated.
As for the last bit, you could say that, but you would basically be wrong. It doesn't end up being very much like a Tyranid organizational scheme.
On the other hand, though, the Tyranids are probably the only army in existence which is better coordinated than the Ultramarines.