This in my opinion is the right way to solve the problem, i.e. provide the customers that want a managed offering the means to get a managed version directly from the entity most active behind the project, (e.g. Hashicorp) while getting the most from the cloud provider's infrastructure. I would be willing to trust Confluent or Hashicorp with operating/managing my Kafka or consul cluster but taking another dependency on their respective cloud offerings should be of concern.
I am quite surprised that its Azure that has shown creativity here while AWS and Google have limited themselves to offering marketplace AMIs/images at ridiculous markups.