I guess that's actually a more general criticism of Heroku in the microservices context; high availability (at least 2 dynos per service) and predictable performance (non-shared dynos, Performance-M at minimum) combine to make the cost of a "production" setup start at $500/mo/service. Non-issue for a monolith, quite tough for small microservices.
(To be fair, we compromise on both of those requirements and use both single-dyno apps and shared dynos, and so Heroku is very affordable for us. But the downside of those choices ends up biting us often enough that I, in turn, end up lamenting about it on HN.)