Supabase developer here. It shouldn't (and doesn't) take a week to migrate 40GB, I'm sure most of that time was strategizing, analyzing, and testing things. Supabase is pure Postgres running on AWS, so migrations are pretty straightforward. Things mostly depend on where you're migrating to/from, and the network latency between the source and destination. 40GB should take minutes in most cases.
A LOT! Probably most.
But Supabase is committed to the free tier and it's not going anywhere. It's crucial to helping demonstrate all the features and the DX to developers.