Like many on this forum I have gone back and forth between email clients trying to find the “perfect” app. For most of us, there is no “perfect” email app so we settle. That is my situation. The closest I’ve come for my needs and work flow is Spark but it doesn’t make the grade for several reasons. Consequently, I’m still using the default Mail app. This has and is forcing me to MASTER ALL of its capabilities and learning to “love” it.
I certainly cannot speak for anyone on this forum but for me, being forced to use Mail has caused me to discovere features that either I did not know existed or had forgotten. One of the more obvious, that one would think I would have paid more attention to but did not, is the column view with bottom preview. This, in combination with multiple Smart Mailboxes, flags, rules, etc., make Mail an adequate email client on the Mac, less so on iOS/iPadOS, but still serviceable. All things considered, I still find Mail, with all of its shortcomings, better for my workflow needs and integrations than third party clients. Of all of the clients I’ve tried, Mail is also the most stable and reliable, and obviously, the most integrated in the Apple ecosystem.