You are right on in the first paragraph, you would need to create a new solution and amend their entities. When you import their changes it will add on any additions to those entities. Importing customizations should never remove anything, you have to do that manually.
Although unlikely, it is possible that the vendor may release a new version that requires you to roll back your customizations and reinstall it. In this instance you would need to come up with an upgrade plan and take into account all of the dependencies of the system.
What the disadvantage here is, is if you create an entity, attribute or relationship in Dev and deploy to forward facing entity, if you then remove that entity, attribute or relationship in Dev, you must "uninstall" that solution. Of course, if you have critical data in that forward facing environment, it is gone when that solution is removed. So, if you deploy from Dev to forward facing, if in the future you no longer need that entity, attribute or relationship, although you can remove it from forms, it will always remain an artifact in your system.
This is a disadvantage when working with Managed solutions.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.