When complaining about lack of resizable/moveable columns please complain about the lack of message threading. "Conversations" is a pathetic excuse for real message threading. You could mention, "Even Outlook gets this right."
And then there is putting the .signature ABOVE quoted text. Signature belongs at the bottom, always. New text in reply also belongs AFTER the words that have already been spoken. Or interspersed between. Is a conversation, or simulation thereof. Words that are spoken first appear at the top. English has always been written this way.
Quoting the attribution no matter it was not said by the person being quoted is also wrong. This is text added in the reply, effectively said by my reply not by the person I am replying to.
What Mail.app gets right is the synchronization of Rules between Macs and use of the synchronized Contacts database. But lately hard to think of anything else it gets right. Mail on iOS hangs a couple times per day and has to be brute force killed and restarted to receive messages.
In addition to everything else it is getting wrong is that Rules do not work on iOS. Back to the desktop one has to select all messages in the inbox and "Apply Rules" to put read messages where they belong.