I think you're overestimating the computation that the client side does. For the majority of web applications the biggest workload is in querying the database,

I think you're overestimating the computation that the client side does. For the majority of web applications the biggest workload is in querying the database, which for any site of non-trivial complexity will tend to come from some kind of server-side API. I also feel there is something to ownership of your tools and platform, and an application strung across several SaaS and a toolset that requires phoning out to different SaaS in order to work is anything but yours.