While I believe I understand some of the reasoning behind the marginally improved "New" Outlook while lamenting the overall deprecated experience - namely, an effort to normalize the look and feel across the desktop, mobile and web versions - the path taken is regressive in nature, at least for those of us who've long relied upon the desktop variant to manage much of their eMail, task and scheduling affairs.
I've been comfortable with the working knowledge that detailed work associated with eMail, tasks and scheduling has been the province of the desktop client, while the mobile and web versions offered very functional and not as detailed abilities.
Now, after having lived with the "new" Outlook desktop client for months now, I can conclude that the 'improvements' to this client when compared to its current and soon former versions is far less capable and far more mobile/web like in function - overall, a deprecated experience.
One notable issue is the mere fact that one can seemingly no longer remove attachments directly from an eMail. While this may seem trivial to some, having attachments to eMail AND the ability to download same simply increases the already arduous task of managing one's documents, while increasing the overall storage footprint (since these could now be stored in at least two places), which could represent increased subscription costs over time.
Microsoft, PLEASE revisit this intended direction for the desktop client, and instead consider introducing some of the long-favored desktop client functions into the mobile and web variants, in turn genuinely introducing "new" functionality all around.