Corrective action without establishing root cause. Which troubleshooting standard is this.
as troubleshooting it happens quite a bit.
It's a matter of economics once reasonable safety has been met.
In the long run the engineers expect to understand the root cause and either fix it or replace with a different design. In the interim one must do something to reduce the risk to the passenger etc. to a level commensurate with all other historical risks (hidden or known problems).
Hats off to Airbus if they understand the Boeing design well enough to have address root cause and thus certified as such. On the other hand maybe they have addressed the risk (against a similar failure condition) with some unique method.
Just because the FAA doesn't understand is not reason to withold a certificate but we as the public certainly are not privy to enough information to comment, except via something like a "Special Condition" published in our Federal Register.