We spent so much time going through other variations on B2P that we know we can't do anything different with it than where it is now. More mana would mean unholy spiking power. Less health means ludicrous HALPMEH loops and the scumming that goes with that.
Bloodmages are designed to be a class that transitions from one playstyle to another through the course of a run. They start out being really great at bursting, everything they have is about storing up resources and picking choice targets, nothing nukes like they do. Then, because that would be far too powerful if it could continue into the lategame, we designed them to transition into a different sort of playstyle - turning their initial resource-using frenzy into less of a scary thing to do through Sanguine turning blood into another resource.
Once Bloodmages finally clicked, we knew we had something that would work for them... Transmuters took about as long to balance, maybe longer. In the end we couldn't make the walls-as-resource model work for Transmuters because walls were less granular than blackspace, so we had to make them give much larger amounts of resources, which meant less ability to limit resource hoarding. Transmuters in the alpha were pretty damn broken.
In the end, Transmuters and Bloodmages took different approaches to dealing with the alternate resource problem: Transmuters abandoned their resource, Bloodmages moved into using it in two opposing ways. Personally, I like the challenge of managing when to transition
