Optimizely's pricing makes no sense for small teams but VWO and Optimize cannot compete on features that start to become very useful as your experimentation and personalization efforts increase.
Any roll-your-own experimentation platforms take considerable resources to make accessible to those in the organization interested in using it (product, marketing, etc.)
In my experience, I agree the core functionality (variant management, remote config, etc.) is relatively small amount of effort compared to the interfaces to make it accessible to those non-technical orgs, like you mention.
However, we found that those interfaces only allow very limited, shallow tests and you very quickly outgrow them as an organization. In other words, once you reach diminishing returns on button color and header text optimizations, you start wanting to test deeper UI experiences and complicated user flows. At that point, you have to involve engineering anyway.
When an organization has engineers who are motivated by business metrics, they have no problem implementing shallow tests (like button colors) while working on tests of the deeper UI experiences as well. And at that point, the non-technical interfaces have little value.
Any roll-your-own experimentation platforms take considerable resources to make accessible to those in the organization interested in using it (product, marketing, etc.)