I think you are wrong. What you say has no sense. If is like you say when you activate Firewall all Internet traffic is locked. Sorry think you are wrong and no sense Firewall block also system app and important app like Google Play Store who keep the phone update and secure.
It's a shame you prefer to make personal comments, perhaps some reading about FWs will make you change your mind ...
I'll reply only on this thread to avoid "noise".
(I'm aware that on Android it seems reasonable not to apply block all by default, however this is common FWs default policies. If default policy is enable all / pass through, it's likely most users won't block all the stuff that is better blocked.
BTW: it's very useful to have a complementary feature that shows traffic and what applications / services were blocked - so that users can block or enable what they wish. If default policy is to enable then traffic or usage can be used to figure what to block, if default policy is to block then blocked list can give a clue what is better enabled)