The only way healer design can be changed is requiring encounters to change. Have more boss fights or rooms like in WP HM where there's a lot of party/raidwide damage going out that requires more than a simple regen/shield to cover. Imagine fights where your entire party has a permanent DoT attached to it. HoTs can cover around 75% of it, but because of that remaining 25% you're still taking chip damage and are requiring heals often. Add in party/raidwide attacks and the usual stupid from players, and it turns things into more of a healing job because there is no moment when you're not taking damage, you're CONSTANTLY taking damage. I'm basing this btw on some bosses and raid fights I've seen and personally experienced as a healer in other MMOs, where the healer has very little time to actually do damage due to how often the party is getting hit.