Wanted to do a test to see what it would take for a "white weenie" deck to be somewhat playable in commander and I came up with this.
Legendary Creature- Human Soldier
Whenever a creature you control with power 2 or less would deal combat damage to exactly one opponent, Ezran instead deals that much combat damage to each opponent.
2/1 My army is my blade.
This card would dramatically decrease the difficulty involved in winning the game by going wide with small dudes and tokens (and this randomly fits into Doran the Siege Tower and Arcades, The Strategist decks) by lowering the threshold from victory from 120 damage across three players to 21 damage to any player... but you can't use strong cards (both in terms of P/T and in terms of being mono-white) and the damage only really counts while an incredibly squishy commander is in play. "Exactly one opponent" is there so the replacement effects don't infinitely ping-pong back and forth if you have helm of the host or a similar effect. If it isn't needed, please let me know.
I expect that this card may be too much but I'm having a hard time seeing the precise cards or strategies that make this card overpowered. Feel free to point out what breaks this.
First, the easy part: you need to change "whenever" to "if". "Whenever" denotes a trigger which it seems you don't want to do.
I am not sure the rules really support replacing combat damage for "other" combat damage this way, but I guess it can be assumed to work with whatever rules changes are needed.
Also, the "exactly one opponent" thing isn't needed. Not really anyway. If you had two of these in play and a third 2/2 was dealing damage, one applies to make itself deal combat damage and then the other applies to make the other deal combat damage instead. Since Replacement effects will never invoke themselves repeatedly (unless a new event is also created in their text somewhere which is rare) the wording is superfluous and doesn't really change functionality. Just note that in that case you are not going to deal commander damage since only one Ezran gets to deal damage and your opponent chooses which one. So it doesn't do well with things like Helm anyway.
My main concern is that this turns into a one-shot kill for the whole table if you can get an army out. Granted, White is the weakest color but "end of your turn, White Sun's Zenith for 20, cast Ezran on my turn, win" doesn't sound appealing. I am not a fan of commander damage as it is but losing to it because someone *else* couldn't block seems pretty terrible to have to deal with. This card means either everyone dies or no one does when you attack with your army.
And even without an army it just allows for incremental damage until you get to the point where a single 2/2 going in unblocked on someone ends the game.
I think this would be better off being a Saskia or Hydra Omnivore ability where Ezran just triggers on damage and makes the creature deal damage to all other opponents or a chosen opponent or something. It doesn't scale as well as your current version because it isn't combat damage (and definitely isn't commander damage) but I think it ends up being a bit more fair with more interesting play lines. The main issue is whether that is truly in white's slice of the pie. It is used so seldom I suppose it could be argued to be.