even UDK kept the block system for fast prototyping. I use it also for making model like objects within minutes.

some engines do not have such a model editor like MED at all, you have to own a 3rd party ones. it's a basic tool, not more. model file formats have to be converted in other engines too, but yes, it could be improved a bit... hopefully i new WED...

terrain editing and object manipulation in WED is not up-to-date at all, probably it is the reason of the development of a new one, hopefully ready soon (in this year ). for me it was not a problem as my original plan was to make my own game specific editor... anyway you can make realistic terrains by some free tools.

I don't understand the collision problems, it works fine for me. or you can use physx too.

a 3dgs asset store would be fine. I would make a lot of expensive content that you could buy unity is definetely an attracting product, but I would need the pro, whose price acceptable only from illegal sources.

it's not a perfect engine, but I have very different problems with 3dgs than you, like a missing quality shader set that works smoothly, integrated navmesh pathfinder (a 3rd party tool is under development fortunately), and the overpriced pro edition that has some great features I would like to see in the commerical edition.