Yours is a personal opinion that is not shared by the majority of DEVONthink users.
The DEVONthink developers, over the years, have devoted almost all of their creative ability to making DEVONthink probably the best tool in the Apple ecosystem for managing your information. There have been some improvements to the user interface and not all have been well-received, but it remains functional without being flashy.
I have been using DEVONthink for over six years and it’s my primary interface for everything I do on my devices. I would be lost without it and wouldn’t change one bit of it though the team behind it continue to improve it in ways I would never have thought of.
David