Yes, exactly, it doesn't follow. You've just re-written your app using a framework that allows you to run one codebase in multiple places, including the web, and instead of doing that, you decide that you no longer want to support the web at all.

They claim a huge reduction in source code line count. After they've just decommissioned their web app...

The web version isn't shut down, but losing crucial functionality. If Flutter let's you run the same code across multiple platforms, then what reasoning is there for one platform getting less functionality after switching to a framework that, if anything, should increase cross platform feature match.

Flutter web isn't production ready, it's false adversiting.