Prometheus is released under Apache-2. There are a lot of people and
companies that deploy Prometheus and even offer it as a service to their
customers, without collaboration whatsoever. And it is perfectly allowed
by the license. Every contribution upstream is therefore a success and a
bonus for our community and our users.

Prometheus strives to be an open project. Not only open as in open source,
but also open as in open and public discussions/roadmap. Everything I
note here is public, links are below.

Amazon Managed Service for Prometheus is actually not Prometheus, but
cortex (1). They are Cortex maintainers (2) (Note that a major
difference between Cortex and Prometheus is that in Cortex, the
companies somehow take a role in decision making (3). In prometheus
governance, we are all individuals).
AWS & Grafana labs have designed and coded the SNS intregration for
Alertmanager (4).
AWS is also committed to provide native ECS discovery (5) and have
upstreamed an ECS exporter (6).
This is only the tip of the iceberg. AWS is also engaged with supporting
Prometheus in the OpenTelemetry ecosystem (7).