It would be nice to have the TestFlight updated with all versions, even if they don’t need testing, so the TestFlight always has the latest version, if it’s not a lot of extra work.
As there aren’t App Store update notifications, it can be hard to always stay on the latest version of the iOS app. A beta may be released on TestFlight but then future minor updates might only be published on the App Store, which means you have to check the App Store page to see when it has a more recent update and then switch to it. Even with notifications, it would require switching between the App Store and TestFlight versions over time as new versions are released, as opposed to being able to have it auto-update to the latest version always.
Publishing all updates on TestFlight would help make it easier to always be on the latest version, reduce expired builds (which you might notice while offline) and allow you to install any specific version you need, in case a hotfix introduces a bug that is particularly disruptive for you.