I think GP agrees with you. They were saying that Scylladb (or redis, or hashicorp, etc.) never would have gotten as much traction if it had been proprietary from the begining. Being open source helped them get where they are, but now they are abandoning open source.

In fact I strongly suspect that this license change will do more than upset existing users of their open source version, it will scare off potential new users and customers. Not only are they no longer open source, but they gave people a reason not to trust them.