I understand what migrations are. I just disagree that they are trivial.
Especially since you need to write the rollback script as well. And then test it with data. And then ensure there are no weird interactions with other migrations. Because if there is a problem with any one of them then it can be a huge headache to unwind everything.
Most of the migrations do not involve fiddling with data (for example adding a column, table). But if they do, yes you will spend more time on them. But it will be on the order of magnitude better then doing the same thing in MongoDB where you just have implicit schema
And I have written many migrations in systems with tens of different db`s/schemas in the same project which could be different based on the geographical region or some other requirement and never had any big problem