That's mostly because D5 is new and adding things the other engines have had for ages :) A mature product always feels like it develops more slowly as the "big jumps" are more likely to happen earlier, and as a product matures with all the main features in place, things become more a matter of refinement. And all that said, I wouldn't describe having access to CPU and GPU rendering as a "snail's pace" development ;) Probably the biggest jumps available these days are AI related enhancements, which Chaos is working on finding good sensible useful ways to implement too. Hope this helps!