Allow parties of 4 in flex

{quoted}

Honestly, that is a bad reason not to add it. As a solo player, I really would not mind muting 4 allies in flex queue every now and then if it means I get fast queue times and priority role selection. I would view it as a potential alternative to normal draft when I have limited time if the rewards are high enough.

Consider that solo players have solo queue, the way to get us into flex queue is to increased incentives and not minimize toxicity in flex queue. Flex queue will never be inherently less toxic for solo players than solo queue. However, it could potentially come with more rewards if riot implements them properly.

Either add party of 5 or keep it.

Normally in a regular community, it would be a bad reason. What you seem to have forgotten is that the league community is a very toxic community, and it has been shown more often than not that teams of 4 do bully the solo player more often than not.