Having tested the mode, here's what I think :
Both teams that relies on synergies (not all synergies are equal) and teams that relies on protecting a carry are very strong and viable.
The real problem is items :
They seem pretty fine at first glance, but the randomness makes them broken.
gives attack speed and stacks infinity (yeah you heard that right : infinitly, so as long as your frontlines gain enough time for it to stack, adc can 1v9 with some lifesteal) +
makes you hit multiple targets.
If you get both on a 3star adc, it's gg. The problem is, you might be lucky and get both, but another player might get 0 drops from his pve rounds. So he'll obviously be much weaker than you. He'll get easy wins in the first rounds, then get tons of win streak gold ==> more interest => more gold => more op champs and more champs on the board.
The snowball mechanic is very harsh so the guy who got good items at the start have huge chances of winning while the guy behind can never catch up.
And your carry doesn't have to be an adc, just have to be a 3 star unit, I once put 3 items on a gnar (attack speed/life steal/tankyness) + shapeshifter synergy (gives him 100% of his max health at transform). He was basically unkillable and was 1v9 everyone.
So I would personally propose this to be fixed by reducing RNG on items and making everybody drop the same number of them. And/Or reduce the number of items a person can have so you have to switch strategically between your items depending on your enemies instead of having a player with 6 items and another player with 1.