Definitely wasn't make or break, but I've certainly been transitioning most of my assets out of Polo because of this and some other oddness I've seen there for the last month+.
They can't be beat for liquidity, but I can't imagine they're not complicit to some extent in market manipulation.
I personally don't believe they are complicit in market manipulation, I think they are just a victim of their own success. However your reaction is the right one in my opinion and OP's wanting to sue them when they haven't done anything illegal is wrong. If you are unsatisfied with Polo transition your assets to another exchange, then they will either have to adapt and become better or another exchange will. As for liquidity even though Polo is the best there are certainly good options available depending on the asset.