Yes, so much worse to have it drowned out by half a dozen threads of a single game than hundreds of little games.
There are arguments against the more general subboard, but that isn't one of the stronger ones...
(Also, didn't ER celebrate its FIRST birthday not long ago?)
If the game is as big as ER, it wouldn't get drowned out in the RTD board (see current state of ER threads). At all. In the ER subboard, the expansion of which I cannot accurately predict, but can venture a guess that it might increase in size, that might not be the case. That's missing the point of the argument, though, as the problem is less that it gets drowned out and more the fact that it gets relocated to a space that has, for maybe many years, been the ER subboard. Let me put it this way:
ER: congratulations! You've become huge and popular. You get your own subboard.
Other, later game: congratulations! You've become huge and popular. To the ER subboard with you!
Not only does it involve moving the game to a board that, whether you like it or not, has acquired the identity of the ER subboard, it carries an unpleasant connotation of becoming second banana to an ancient behemoth simply because it came before you, and possibly a distinct feeling (unvoiced, probably) that the new game isn't all that welcome there.
We have hundreds of threads within the RtD subforum, and I can't say that threads go too unnoticed in there despite the fact that ER is huge, along with some others games. I do see where you are coming from, however, but I still support the huge-type subforum ideal, because I doubt ER will reach an amount of threads that drowns out any other game placed in that subforum. Besides, if another game comes along to reach the size of ER, it's probably likely that people will already have invested their attention to this game and want it moved to the subforum for organization. Creating multiple subforums will make subforums seem, at most, 10-20 threads long.
((I am also half-playing the Devil's Advocate here, offering opposition for the sake of opposition at some points. But I do truly support a general subforum.))
As for ER's hugeness, we can't use the present situation as a suitable reference because ER is still only three threads wide (well, I suppose four, counting this one). If it were eight threads, we'd have more of a problem. And, as I mentioned, the problem isn't so much getting drowned out by ER as the fact that any other large games would be put somewhere that is solidly ER's territory. Besides, just because a subboard is 10-20 threads long does not mean that there shouldn't be one.