Hi @jarthda
The image in the reference below depicts well at a high level the key Power Platform components.
https://docs.microsoft.com/en-us/powerapps/maker/common-data-service/data-platform-intro
The 4 key offerings (BI, Automate, Apps, Virtual Agents), with key underpinning services such as CDS, Data Connectors, and AI Builder.
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While not depicted above, these services all sit on Azure. While not required to use all of these discrete services, they are natively integrated and can be combined to provide business needs across several key areas.
So it's tough to answer your question of which is cheaper or more performant as they serve different purposes.
If we go back to your original concern about data migration, Dataflows are well suited for citizen devs to do low code ETL into CDS, but is still in its infancy and not ready yet for high throughout / enterprise data migrations.
If you're looking at migrating complex and/or large data volumes and are more technical, then a data integration tool like SSIS + Kingswaysoft or Scribe is designed precisely for this sort of use case and can get large data sets into CDS without much trouble.
Note that I am not trying to sell you on SSIS/Kingswaysoft, I just list it as one possible solution and I have experience with it on a few data migrations in the past and with current system integrations and it has worked well.
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