Making good games needs a lot of time, knowledge and experience. If you lack one of those things, you won´t be able to create good/complex/big games. There are endless tricks to make things fast and if you start with doing the worst thing possible performance wise, which is alphablending with lots of pixels, you do something wrong.

About the 6 Zombie example, what shaders do you use, how are the zombies animated, are you using stencil shadows?
99.99% of the shaders around are extremely slow, because they where never really optimized in any way and just thrown together by beginners, as for example me 5 years ago. Bone animations on the CPU are also very slow, because it needs your vertex data on the gpu to be updated every frame, while doing it in a shader is a lot faster, especially in combination with tangents, depending of your models, this can speed things up like 10 times and a best case scenario. Stencil shadows in gamestudio are really slow. Don´t use, or use very lowpoly meshes for them.

Edit: There usually is a reason if things are slow and most of the time, there is a solution, which has nothing to do with the engine.