I think it depends on where you want your semantic model to be and how you will managed the governance. PBI can be your semantic layer if you use premium/ppu + xmla so you won't need SSAS tabular unless you have a clear on-prem or governance reasons.

With premium/ppu + xmla you can read and write, get partitions, incremental refresh, calculation groups, perspectives, translations, OLS/RLS, TMSL and read replicas in the service.

You will need a gateway if your source is on prem.

Keep in minde that governance needs discipline and you should standardize on centralized and certified datasets.