I'm curious: what was the high (or low) point for the "required dedicated healer"? In other words, when was it most vital for the party to have someone who was all heals, all the time? I'm guessing 3.X, but would like to hear from others who have more experience with earlier editions.
3.x had WoCLW, so there was plentiful, cheap, between-combat healing.
Low-level 1e, everyone depended on the Cleric's first levels spells (plural due to bonus spells for modest wisdom) to all be used for CLW, every day, including days off when everyone was recuperating. Height of the "Band Aid Cleric," IMHO. (Not that 2e
really backed off from it, that I'm aware of, but I skipped the last few years of 2e, so there may've been something...)
Before that you couldn't depend on the Cleric, initially, as he didn't get spells until 2nd level, and didn't get enough to keep everyone going. After AD&D:
3e: Clerics could cast healing spells spontaneously using any spell level slot, so in-combat healing was always on the table & in demand, and took their full action, but could be largely eschewed in favor of cheap/plentiful WoCLW (& WoLV) between-combat healing. So there was still a 'healing burden,' but it left a lot of room to go all CoDzilla on the campaign, because clerics got a lot of spells, presumably in the expectation they'd use lot more of them for healing than actually worked out.
4e: Everyone got healing surges they could use to fully heal up between combats, and could Second Wind 1/encounter. Defenders (Fighters &c) also often got at least some self-healing. The 'leader' (Healer) role mostly triggered those surges, with a bonus, using minor-action powers compatible with any other full action, and/or riders on otherwise meaningful powers. Item healing (until late post-E) also consumed surges, so there was no WoCLW effect trivializing healing as a resource.
5e: Everyone gets HD, and can heal between combats, but not in combat. The fighter gets one self-heal feature that scales poorly. In-combat healing uses slots rather than triggering HD, and either takes your action, or takes a bonus action and restricts what you can do with your action, so the 'healing burden' is back, though writ small compared to the TSR era.