Proton engineering culture always got a bad rep pre-AI era as well(per their glassdoor reviews[1]) . Poor engineering directly or indirectly makes them susceptible to data breach because good talent stays away. One reason why I hesitated moved to proton back when a lot of people did. My understanding is that the only reason they are in the game are because send email services are extremely difficult to run.
[1] https://www.glassdoor.com/Reviews/PROTON-Reviews-E13574.htm