It's also important to look at the importance of each series as a whole. For instance, a small series like Xenoblade or Golden Sun probably wouldn't get more than one character, despite having a number of supporting characters that could be called important.
I didn't say they should unintentionally try to have the same number of reps per series, that would be unreasonable. But there are certain characters within certain series that at least deserve more serious consideration, like Dark Samus for instance.
Thing is, though, is Metroid important enough to warrant that 4th slot? So far, the only series to get that many have been the Big 3(Mario, Zelda, and Pokemon). Is Metroid as important as those franchises? Sure, it's as old as Zelda, but it has a spotty attendance record(missing out the N64 entirely), and its popularity, while decent, doesn't even approach the level of the three I mentioned.
Four? No, three. Samus, Ridley, and Dark Samus. That, to me, seems reasonable, and well representing of the Metroid franchise.
While sure, it may not be as popular as the big 3, only having had Samus up until this point has been nothing less than negligent.
If it were a popularity contest we'd have nothing but Mario, Zelda, and Pokemon characters with a few others scattered about. If Smash were a popularity contest, we'd never have gotten Captain Falcon(who is popular BECAUSE of Smash), or any Mother or Fire Emblem characters. We also wouldn't have G&W, R.O.B., or the Ice Climbers.
50 characters is reasonable, yes. However, it's ludicrous to think that we'd get much more than that, or that 50 is somehow the "minimum." There's more to Smash than just the roster.
You're taking what I said all the way to the extreme, first of all.
Much in the way series like F-Zero, Mother, Fire Emblem, and the retro series were included and in a way Revived via Smash, that initiative, if you will, has not been utilized to it's potential. We still have Advance Wars, Balloon Fighter, Golden Sun, Mach Rider, Legendary Starfy, Sin and Punishment, Punch-Out!!, Custom Robo, XenoBlade, etc that could receive the same treatment.
Having a bunch of assist trophies frankly wasn't good enough, especially not after having been teased by such consideration and digging as was so graciously utilized via including F-Zero, Fire Emblem, Mother, etc.
They started a fantastic trend, and kind of dropped the ball with Brawl. Why? Who knows. But trust, thinking that certain characters should have been playable by now is by no means ridiculous.