I feel like the most important factor is UI consistency. If the UI changes, it costs so much time and re-learning. Thunderbird has mostly been the same since m

I feel like the most important factor is UI consistency. If the UI changes, it costs so much time and re-learning. Thunderbird has mostly been the same since many years. The only thing I noticed is, that the quick search has become buggy and scrolling in the inbox takes a second to load the titles.