That's the issue with every 'fun' mode though, they aren't balanced, and once the broken picks got figured out you get a hard meta that has no place for anything else.
Other than that, it I think it should be on another map than summoners. On SR, you usually get the entier game decided on the lane matchup. a bad matchup in lane for one for all leads to 3 loosing lanes and often not even a jungler that could win atleast one, so most OFA games are decided by picks already, and then SR also just lasts to long.
If it instead took place in TT, Howling abbys or the crystal scar, laneing would be less relevant and you would have skirmishes and teamfights alot more often, and it woul overall be alot more fast paced so you're not stuck in a impossible matchup for as long.
Also, in OfA you often have people beeing bad at or even unwilling to play a given champ, so it naturally tends to suck if you're not premade.
They just should open it up as an option for custom games, same with Urf mode, so you can use those together with friends or some strangers that have a similar mindset for some fun brawls.
Back in the days, that worked quite well with aram.