AlmostLegendary, you really need to get away from the idea of "neutral" stages and get with the idea of "starter" stages. That's what this is about.
And Diddy IS artificially buffed by the smaller starter lists.
I'll try to lay it out as clearly as possible here. Diddy has been stated to have BF, FD, SV, and PS1 among his best stages.
A 5-starter stage list gives Diddy the ability to start on one of his BEST stages. This is clearly a disproportionate advantage when compared to other characters.
Let's say for example, we have a character that does extremely well on stages like Delfino, Halberd, Frigate Orpheon, and other stages with counter-picks tendencies, but are still starter stage material. If we had a stage list where 3 of those stages were starter, along with FD and SV, for example, this character would be ARTIFICIALLY buffed, because he gains the ability to start on a COUNTER-PICK. The idea of "neutral stages" needs to be moved away from. We build a starting stage list such that it distributes advantage evenly, not so that we play on only flat/plat stages with no hazards.
The goal of having 9 starters is to mitigate the advantage gained by any one character. Diddy is a great character, but his stage versatility is low, which hurts him overall. If Diddy is given the ability to start on a stage he would use as a COUNTERPICK, something is out of balance.
9 starters restricts his ability to start on a counterpick, but he still has control over WHICH of the additional "counterpick-esque" stages he wants to go to, since most (if not all) of his opponent's strikes will be used on FD, SV, BF or PS1.
Diddy is still a good character within the 9-starter system, because he still has a strong influence on 4 of the 9 stages that would be commonly used. The idea is to make it so that no character receives a counter-pick stage through stage striking, since the goal of stage striking is to get the FAIREST STAGE FOR THAT PATICULAR MATCH-UP. This doesn't mean the stage where the match-up is even, this means the median of bias between both characters.
As an aside, Meta-Knight becomes a huge problem because he has NO BAD STAGES. He becomes extremely powerful under any counter-picking system because he has the ability to remove your best stages with little concern for what stage he goes to. Strictly speaking, MK can counter-pick and stage strike offensively.
However, I don't believe the fact that a 5-list restricts MK (which it doesn't) is valid grounds to keep it. Meta-Knight is JUST another character. He deserves NO special treatment when compared to the rest of the cast. As such, the fact that he excels under this system is not a fault with the system, it's a fault with the CHARACTER. If this extreme advantage is enough grounds to ban him, there is no reason to be restricting him unfairly when compared to the rest of the cast.
We don't build the system such that we can keep him. We build the system such that it is FAIR, and if he is too powerful to fit within the system, he is bannable. Simple as that.
We don't build the system such that we can keep him. We build the system such that it is FAIR, and if he is too powerful to fit within the system, he is bannable. Simple as that.
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