They have been the same team for the past 2 years. I think they have done a pretty good job developing new features thoughtfully and improving the user experience. One thing I’m really enjoying about this release is that they have made it much faster to toggle between accounts.
If they are confident adding their branding, then I take it as a show of confidence in their work.
I’m not sure, but that could be connected to the name change K9➡️Thunderbird. They have said that they will maintain parallel releases of both (identical except for the name/branding) for the immediate future. This release appears to be the identical but may (or may not) solve the issue.