The correct way to do this: Heroes work differently in different maps with different objectives.
But this carries too many problems with it that also makes it too complicated. Really, when it comes to AoS games, different maps already means a completely different game. Remaking every single hero to be viable in this another format is a task far too impossible to fathom. It is far more plausible it will be just like Twisted Treeline.

Riot remaking their game to fit the new map is not impossible, but it is not plausible.

Balanced Dominion Aura Item 500
Ruby Crystal (475) + Recipe (25)
+250 health
Unique Passive: Nearby allied Sorakas get +100 AP
Unique Passive: Nearby enemy Shacos get -100 AD

There, balanced with just items! ^_^

I don't see why it matters if certain champions are more viable on one map/mode compared to another, as long as they're not ultra trash never pick or something. I guess some people who really love champion X would QQ a lot of X was less viable in a different mode, but that's pretty silly.

If LoL continues to expand in terms of maps and game modes, I can foresee balancing becoming both more difficult and simpler, because at a point it doesn't matter if every champion is viable on every map. For example, if you have 100 champions and fifty are viable on each map, that's pretty **** good.

yall sure did alot of balancing and know what your talking about.