Dahbomb said:
X Factor undeniably adds another level of depth and strategy to the game.
At the same time it lessens strategy, and thus removes depth for all those other "levels". By making comebacks (much) easier it devalues all of actions made up to that moment. To get specific: certain guesses/choices(not answers, but instances) being able to obsolete a large groups of guesses/choices simplifies the tactical nature of a game. X-factor is just too important, and only so many things can matter during a match(or an entire battle system). This isn't a question of balance, so whether both players can use it doesn't matter. But then again, one cannot deny the (spontaneous, unearned) momentum of a XFC lvl 3 character (especially if the opposite player only has access to XFC lvl 1 or 2).
There is nothing WRONG with 3 v 1 looking bleak. It is amazing and disheartening how this isn't universally accepted among knowledgeable players. Consider what you have to give up for it not to be a case. Rubber-banding is horrible! (Except for when you are playing with children.)
Though comeback mechanics are not entirely evil or anything. Certain qualities of X-factor are still nice because they prevent chip kills and prevent landslides. That keeps 3 characters + 4-5 meters v 1 bleak rather than impossible. (EDIT: I should clarify on "landslides": Basically it leaves enough wriggle room in situations like Storm with 5 bars. At which point the match is over once she uses it once.) It is when x-factor makes you offensively superior does the whole thing derail. Compare to a "burst" mechanic, which only saves a player damage rather than putting him in an equal or superior (offensive) position(which is actually sometimes the case in MvC3). There is also a solid solution to make bursts fail, by baiting them.
Here is a fun activity: Put X-factor(lets say based on a combination of low health and rounds lost. Under 50% + lost a round = lvl 3) with all its bonuses in other fighting games. Health recovers, no chip, deal +50% more damage, faster frames/less punishable/easier combos, canceling blockstun(in SF2 lol). That game now better? God No! But it would add a new level of strategy though! lol
Don't get me wrong though, XFC doesn't break the entire game. And the game is a lot of fun. It would be more fun without it(or, really, certain aspects of it).