MK will win on any stage. Only shot Ike really has is Pirate Ship and maybe Green Greens.
Halberd is neutral. Extremely easy to dodge hazards, predictable flight path. Probably more neutral then Delfino or Siege overall, if only for lacking walk-offs after the very first part.
The CP stages are perfectly fine. Needs JJ and PS and then it would be perfect, but it's good. I can understand PS not being included.
My main point with Snake was that his best stages were almost all neutrals. It doesn't matter who you are, in the five stage system it was almost like he had CP advantage right off the bat. Battlefield? Amazing Snake stage. Smashville? Amazing Snake stage. Final Destination? Amazing Snake stage. Lylat? Another very good Snake stage, sometimes neutral. Halberd is as well, though less likely to be neutral.