Remember, Steam is only a gateway to the MS-Installer. Regardless of Store version, the MS-Installer is the one doing the bulk of the work, including the 1.6GB base download.
What you’re mitigating by going to Steam is the convoluted interdependence between MS-Store, XBox for Windows and Windows itself. Changes in any of those systems in an MS-Store version of the sim can prevent it block the sim from either launching or updating, usually without a diagnostic message.
For the most part, Steam only requires you to tie the license you bought for the sim in Steam to your XBox for Windows Gaming Account (Gamertag) once - when you first buy it and launch it form Steam. After that, access to the sim either launching or updating is NOT dependent upon pending updates in MS-Store for example.
What is common to stopping both versions from launching or updating?
Pending Windows OS updates
XBox or Playfab Live Services failures or degraded services
Refreshing your XBox for Windows and XBox Live login sessions by logging out and in again