Tray implementations are actually on the horizon - recently taking shape with the help of community developers. For example Bug 2023000 - Implement Linux system tray: hide-to-tray
You may be confusing IMAP+js with pop+js. Pop is running as js, but the IMAP rewrite was abandoned early. IMAP will likely be rewritten in Rust in a future year.
Yes, FUD and long held myths can be found anywhere. But speaking as a staff member and someone who has seen first hand user reports, here is some straight shooting:
* there are rare cases of a profile either misplaced (exists but not correctly pointed to) or gone - it is something which I understand Firefox people are working on (Thunderbird uses the Firefox profile system)
* there are extremely rare reports where prefs.js is corrupted
* there are no compact failures in current versions - there are no open bug reports for recent versions, so it has been totally obliterated by a rewrite and subsequent fixes. Most user reports of compact failure are attributed to other causes of folder corruption
* folder corruption can occur as easily from external sources as from product bugs.
Also, beware drawing broad conclusions about other users' experience from one's own personal experience. I have almost never experienced corruption - once in the last 10 years. But I am also using a Thunderbird profile that has gone through 5 different laptops, two different OS, using daily builds, which is AMPLE opportunity to have had multiple catastrophic failures. But because I know other users experiences I consider myself lucky.