I guess I'm just not seeing the drastic effect that the stage list changes are making. Admittedly I'm not a Marth player but of the three most common starters (Stadium, BF, Smashville) only PS2 seems to be skewed in Fox's favor from what I know, and even then there are PM Marth players that either counterpick Fox to PS2 (Axe) or at least switch to Marth when being counterpicked to PS2 (Emukiller).
As for the idea that Marth has to ban Dreamland, Norfair, Yoshi's Brawl and DP... lol what kind of godawful stage pool is your scene running? Just because certain stages are viable in a vacuum, doesn't mean it's a good idea to make them all legal at the same time.
And I honestly don't think Marth's CP options are worse in a bo3 than they are in Melee. If he bans FoD and FD you can take him to Yoshi's Melee and WarioWare.
Atleast in melee, pokemon stadium has been currently perceived as being marth favored against fox. Combined with fox nerfs and the lack of stage transforms, which used to favor fox and now marth doesnt have to deal with that, it is probably even more in marth's favor in PM.
FoD however can be argued to be spacies favor, and not marth nowadays.
Personally, in the matchup I would much rather be marth in pm 3.5 and melee, but I can see how the perception in this matchup can be very controversial. I also prefer marth vs fox more as marth in PM compared to melee with the change in character nerf/buffs and the change in stages considered.
This is not really shots against anyone in particular, but I think people need to judge fox more of how he is practically played in the meta with good players of similar skill (which I guess is rather hard to define) rather than arguing about some theoretical TAS level fox combined with top level players who have been playing this game for years and then comparing it to the characters of players who may not have played this game all that long and don't have 10+ years of experience with their character.