[lhorie]

You kinda have to have worked with Flow to understand where this comment is coming from. Basically what tends to happen for Flow upgrades is that some upgrades throw a million new errors with incoherent messages. For things that are already verified to be working and in production. So an upgrade essentially becomes an exercise in making the type checker happy for its own sake, at the expense of not implementing features or fixing real bugs.

Typescript does not have soundness as a primary goal for a very good reason: there's a trade-off between soundness and productivity, especially when threading the large gray area between theoretical soundness and the realities of what constructs the compiler implementation is actually able to handle and what the existing ecosystem throws at it.

What the GP is lamenting is that a lot of changes in Flow create more work for developers, but they don't improve the rate at which it catches bugs in practice.