I don't think Demigod will ever be Balanced.
It's like Rock Paper Cisor. With Sedna + Erebus there's at least 8 different playstyle possible.
Sedna full heal or Sedna + Pets or Sedna tank build and again the same for Erebus.
I don't even understand how you can loose with TB + Regulus against them.
You just have to set a mine field and lure erebus in it then stun bolt bye. Erebus instant kill without even the slightest chance for a heal. So before crying imba. 3 Words.
LEARN TO PLAY.
We played 10 games today with 2 of my friends. First game was a 3v3 on prison. QoT + Regulus + Erebus against TB + Sed + Ub.
They forfeited in 10 minutes, saying that Qot is imba. Then we swapped team, they took our DG we took them, same result. Some people just have to find a reason when they loose. Lag, or crappy teamates, or imbalanced game or whatever. No man, if you loose, think about how, and what you could've done to beat them.
So yeah in 2v2 with equal skill, sometimes it's rock paper cisor. The DG pick will decide if you loose or win, but that's part of the game, trying to find the best combo against X or Y team.
Sedna is very hard to kill because she has a lot of +regen HP + heal. So many options to counter that...
Drain her mana or Use the item to reduce her regen hp by 75% or stun or silence and you name it. You just have to use your brain and figure it out.
Edit again : How a imbalanced game will be troublesome for leagues anyway? Dota is the closest example. How many heroes are actually played in leagues? 25-30 out of them all. And oh Dota is played a lot in league and E-Sport. And guess what, competitive players almost never whine about imbalance.
And most of the time if there's a great imbalance due to an exploit or something, it'll be written in the rules :
-No monk Stacking
-No Heart of life during Shield/Invuln
-Healing wand limited to 2 per team, Tp symbol 2 per team etc.
That's an example. And most of the times devs will react and will fix this behaviours.