I settled up on AWS ECS :)
My main issue with Heroku was that they have not changed anything in _years_. No support for gRPC, no IPv6, and simple VPC peering costs $1200 a month.
They just shipped HTTP/2 terminated at their router [0], and have it on their roadmap [1] to support HTTP/2 all the way through. But it seems like it's at minimum a few months off.
(As for VPC peering: the moment you need that, it sorta feels like Heroku is no longer the right place to be, even ignoring the costs.)
[0] https://blog.heroku.com/heroku-http2-public-beta [1] https://github.com/orgs/heroku/projects/130