"Stupid" is a highly relative and subjective term when you're talking about the game series that gave us the Green Missile attack.
The nature of the character select screen means you probably aren't expected to like everyone that's on it (case in point: the Star Fox shenanigans in Brawl). It's the argument of size itself that I find more "stupid" than arguing against Ridley as a character, because it shows a lack of imagination. Game design gets to be very boring if nobody behind it knows how to bend a few rules, or defy someone's expectations. To me it's exactly the same as when people used to say that Mega Man shouldn't have been considered because he'd be too similar to Samus (or Kirby).
Why would anybody think Megaman wouldn't be more original, he can shoot while moving as opposed to Samus needing to stop and charge, and why would people think Megaman would be similar to kirby? The Power obtaining? Last I checked he needs to kill a robot to gain a new power for the most part, its not the TV show.
Ridley
is stupid. Like Sakura said, its basically Wishfulfillment and while a lot of crossovers do that, not all of them do and at times they'll snub whatever character for a more popular one. I'll refute again that Metroid doesn't need more than Samus/ZSS to represent the series as a playable character, it fits with the lone bounty hunter image, she's the most important, and honestly, only important character outside of the Metroids themselves.