Yes, I understand that, the expertise point is very pertinent indeed. I am not against using available engines at all. My main point is still that this should

Yes, I understand that, the expertise point is very pertinent indeed. I am not against using available engines at all. My main point is still that this should be a decision that you make when starting a project, not one that has presumably been made for you. Team members expertise, project cost, for how long you'll be using the tech you're developing, etc. should all be taken into account. A practical example: Imagine trying to optimize loading times when the whole resource system is a massive generic thing that has been made for you. Now imagine having to support a new platform. You could be in a bind simply because you're using third-party tech (especially if closed-source).