> This is true, but is it really a show stopper?

I can’t comment on their data model but in my own experience partial indexes are an invaluable feature. In particular partial unique indexes as it both expands the guarantees of your data model that can be enforced by the database while taking up (what could be) considerably less space.

>> As a side note – we don't use MySQL ourselves

> I think this is the real reason. They just didn't have the necessary talent to implement the features correctly. Wrong schema specifications and not knowing to implement nested set patterns is a sign that they don't have a knowledgeable DBA on staff.

This must be the big one.

Given enough experts and a drive to make it work, technology finds a way.

Given no experts and not enough users to complain or care about breaking compatibility, technology finds the door.