I don't think it's a bad system to build on, but I would be nervous to have it as the only option in my tool belt. Proprietary cloud services often create vendor lock-in, and the skills you learn eventually become non-transferrable as you get more invested in their system. If you only want to work at serverless companies, or on serverless projects, that may be fine. But, knowing how to SSH into a machine, maneuver around, and how to set up a server will always be valuable