Here's the problem with your suggestions: How do you create content around how players will play it? If certain healers cannot or struggles to meet the healing demands of certain content, then that healer will not be played. That also limits design possibilities and possible skill expansion. The healers we have now all generally touch upon those various healing aspects in some way. As healers get more tools, they will get more oGCD heals or expansions to their current gimmicks. Forcing them into a single aspect could mean an increase in dps skills and expectations, but anything that requires a lot of healing (usually the last fight in a tier) will be almost impossible for them to handle.