I see well your points,
Just would like to mention, moving from any saas/ pass/ iaas to self service or other vendors solutions has a cost, but that cost depends on the level of benefits that you had during that usage

I don't remember a customer moving from AWS to other providers in last 10 years, and if rarely are, they will planify a migration,

AWS serverless ecosystem add high level of coupling to vendor but remove high level of coupling in design and save you lots of costs during years,

But at the end , AWS lambda is not one-size-fit-all solution, it must be used with a precious care for appropriate usecase and AWS step function (my most prefered AWS service) as well.

Using ecs and fargate is another serverless solution but with a more level of maintenance and effort and I m agree it must be used instead of lambda in many usecases that lambda doesn't cover the design important pillars

Vendor lock in vs mental lock in

Not being mentally locked in is important as well

Thanks sharing your point of view