My opinion has always been that I like what the Module::Build folks are trying to do, but I hate their attitude. The example that I point to of that is their trying to push people away from using the simple compatibility layer because they want to guarantee that people hear of Module::Build. It seems to escape their attention that they are guaranteeing that people will first hear of Module::Build by being pissed off, and this isn't a very good thing.
I'm not sure where you get this from. The only time I see Ken discouraging people form using the compatibility layer is when there is something that cannot or will not be emulated by Module::Build. For example, Module::Build's compatibility layer doesn't emulate MakeMaker's PREFIX stuff. Ken decided not to do this because the way this is done in MakeMaker is insanely complex. M::B does offer a comparable feature (install_base=...), but it's much simpler.
I've never seen him tell people not to use the compatibility layer in their modules, and in fact I recall that he and I actively worked on it a long time ago, and he continues to work on it now.