So the immediate cost to Airbus of grounding the fleet is quite low, whilst the downside of not grounding the fleet (risk of incident, lawsuits, reputation, etc.) could be substantial.
"We take proactive measures, whereas our competitor only takes action after multiple fatal crashes!"
As far as I'm concerned it has not helped with their marketing.
It actually inspires a lot of confidence to people who can at least think economically, if not technically:
Grounding thousands of planes is very expensive (passengers get cash for that in at least the EU, and sometimes more than the ticket cost!), so doing it both shows that it’s probably a serious issue and it’s being taken seriously.
With that out of the way, being expensive does not preclude shoddy work. At the end of the day, the only difference between "they are so concerned about security that they are willing to lose millions[1]" and "their process must be so bad that they have no other choice but to lose millions before their death trap cost them ten times that" is how good your previous perception of their airplanes is.
I think that, had this exact same issue happened to Boeing, we would be having a very different conversation. As the current top-comment suggests, it would probably be less "these things happen" and more "they cheapened out on the ECC".
[1] Disclaimer: I have no idea who loses money in this scenario, if it's also Airbus or if it's exclusively the airlines who bought them.