However, Outlook is very much actively developed and myself being a Premium user am receiving new features now and then, like UI refreshes etc.
[0] http://journal.stuffwithstuff.com/2015/02/01/what-color-is-y...
Something that scales with mailbox size, network latency or similar is happening on the UI thread in Microsoft Outlook. This boggles my mind every time it happens, which is every day.
Something tells me Outlook is a huge pile of legacy C++ that no one dares rewrite any major part of even in the face of issues like this.
The Mac, web, and mobile versions are getting a whole lot of feature releases in comparison to the Windows client, but virtually all of them are intended to bring those other clients to feature parity with the Windows client. I've interpreted this as more of Microsoft treating these alternate platforms as first-class citizens finally, rather than as neglect of the Windows clients.
This also isn't limited to just the Outlook client - it's a trend across the entire Office suite. For example, Power Query[2] is a really neat and powerful ETL system hiding within Excel (as well as used in PowerBI, and originating in SQL Server Analysis Services). It's been available for years in Excel for Windows, but only recently became usable on Excel for Mac thanks to a major refactor[3] to port it to .NET Core and strip out Windows dependencies. Eventually this will reach feature parity with and replace the legacy Power Query code in the Windows Excel client, then all net new development will be cross-platform and available on both clients simultaneously.
All things considered, I view the resource allocation across the platforms as a positive. Presuming the feature development happening for the non-Windows clients are as similarly cross-platform as the Power Query effort, it'll eventually lead to cleaned up Windows clients with decades of legacy cruft refactored out, feature parity and consistency across platforms, and substantially greater velocity as those resources currently split between platforms eventually consolidate and focus on a unified, cross-platform, and cleaned up codebase. And if the refactors continue to prioritize .NET Core, it also bodes well for an official Linux client eventually.
[1] https://docs.microsoft.com/en-us/officeupdates/semi-annual-e...
[2] https://docs.microsoft.com/en-us/power-query/power-query-wha...
[3] https://devblogs.microsoft.com/dotnet/using-net-core-to-prov...