The problem is that when you you need to tell the planner what to do, you can do it in MySQL, but not postgres. Imagine you've got a production database with lots of traffic which suddenly can't handle anything because it inserted an extra row which tipped the balance and now takes seconds to process a common query.

Do you know how to fix the table statistics quickly? Do you know how to change that query to force the execution plan you want? Do you know how long the solution will last until the stats change again?

MySQL is a bit more predictable for this case and if things go really bad for some unexpected reason, one comment can fix it.

I'm looking at it from ops perspective. The ratio during development doesn't matter that much - all issues are solvable at that stage. For me it's rather "which situation would I rather be in at 3am".