Yes, Classic Mode unlocks are preset.
I kinda figured something like that, but only Classic Mode ones are locks, huh? So any others are just kinda random?
Like, I just used Link in a Spirit Battle and got Zelda (yay).
Dead is an understatement. It's straight up extinct.
Pretty much..
I don't know about that. Marth and Roy were the farthest thing from world renowned when Melee happened. You could say the same for Corrin partially. Characters are added for different reasons. I believe the same applies to 3rd parties, Bayonetta being the biggest proof of that.
I do think there's a risk of alienation with a MK character, but they know better than me when and how to pull the trigger.
Marth & Roy are a different beast altogether, they are in the base game that was going to sell regardless, the series is big in Japan, and they were originally going to be Japan Exclusive until they proved popular with Playtesters/Nintendo of America or something along those lines.
Corrin is from Fire Emblem, which was, and is, doing gangbusters WorldWide. A new character, yes, but not unknown since many people already saw the base design artwork for Fire Emblem Fates as well as all of the pre-promotion, trailers, etc for the game, which was already released in Japan.
For Bayonetta, she's also not a virtual unknown amongst gamers, even I knew who she was before actually playing any of her games. Heck, she was even expected by a lot of people to be in the base roster for Super Smash Bros. for Nintendo 3DS/Wii U due to Nintendo's involvement in Bayonetta 2.
Yes, Corrin & Bayonetta were for marketing purposes as well, but they weren't virtual unknowns or dead franchises in one part of the world by any stretch of the imagination.
Also, as a cultural thing, Japan tends to care more about Japan, so Nintendo & Sakurai are more likely to pick characters that are popular worldwide and are of Japanese origin..not to mention Sakurai likes to plan and discuss how a character will work with the team or person behind that character, so there's that too..language barriers are a big hurdle.
I'm simply saying that they won't likely pick a series that's only popular in the West when they can pick a series that is more popular worldwide.