FWIW, I do use Lightning all the time and only know of a couple of minor UI bugs, and at least one other person in my house uses it to sync with external calendars routinely without serious problems as well, so if there are serious bugs there then they don't seem to be universal. In any case, I'd much rather fixing this sort of thing was the priority for the project than yet another UI theme overhaul because reasons.
The order in which you install add-ons, such as the provider for Google calendar and Exchange calendar support, matters. I've spent too long jiggering with add-ons to get them to play nicely together.
Once I have a functioning setup,I copy the profile wholesale from machine to machine. I use Thunderbird every day and have done for years.
