All of your points (minus maybe the first one) should be "easily" solved/implemented in a company the size of Atlassian, and maybe there are newer costumers sha

All of your points (minus maybe the first one) should be "easily" solved/implemented in a company the size of Atlassian, and maybe there are newer costumers sharded like this already. IMO what happened in this case is basically tech debt that is now being paid with loooot of interests.