Well I'm sorry if mana was too hard for mere mortals like me to manage at that time, but that's my opinion, haha... I have healer friends that raided in Vanilla and they share my view on it.
Maybe things like these made some encounters hard due to it's length, but MOST of them were considered nearly impossible due to the "holy shit how do I play this game" aspect of it and the lack of skill from most of the raid! I understand what you said about it really being hard, but you have to agree that if people did their job, you probably shouldn't have to heal so much shit going on.
The mana bar is "like an energy bar" these days because there is insane dmg going on in some encounters and it'd be nearly impossible to heal without that amount of regeneration. I can't say much because I haven't had time to raid that much this xpac (altought I'll start raiding tomorrow, finally), but it's easy to notice that in most heroic encounters. Even with the insane regen, you can see a ton of healers going Oom in encounters like Lei Shen, etc.
In addition, i'd like to quote Dazzy here:
I mean, from what I know vanilla was hard mostly because of stupid people, so yeah!Finding competent people is the only truly hard boss in wow.