Don't forget the Divine Aegis. This is actually tilting the tables quite a lot in the favor of discpriests.
That said, mana efficiency isn't the most important thing here (otherwise we would only be casting Heal). Throughput matching the damage spikes is. An infinite mana holypriest is a beast of a healer, probably the best healer in the game. But there is absolutely nothing wrong with the HPS of either specc when they can go all out. Holy can definitively go more "all out" than a discpriest, though.
I consider this the core of the specc design. A druid have two very defined "overdrive buttons". They rely on personal cooldowns like ToL and Tranquility if they need to go all out, but don't really have to do this very often since WG is ridiculously cheap and effective. The major complaint of druids right now is that they worry about how to deal with raiddamage phases when WG is less of an answer to everything and the alternative heals are less godmode. Bottom line is - druids are cooldown based healers when they need to go all out.
In comparison, a holypriest don't really have an all out button. Our current all out button include Divine Hymn (which typically lowers your HPS right now) and Guardian Spirit (one target only). Very few holypriests take AA since smite/holyfire is so worthless as holy. What we do have is a large toolbox of heals. None of them are remotely close to WG when it comes to efficiency, but Prayer of Healing in particular is spammable and without a cooldown. They also cost a crapload of mana. Any holypriest can empty their manabar in less than 30 seconds if they go all out with serendipity rotations. But the HPS will be insane.
I fully believe this method of healing is the holy overdrive button. Just go all out and use those big heals nonstop. It's not a bad design idea, because we are at the end of the day limited by mana, just like druids are limited by cooldowns. What a holypriest don't have right now is a fallback. When you are oom, and you will be, you are left with Heal. Which is pretty much worthless for all raiding content. There is no mid-sized heals in the holypriest arsenal. If WG is a short-term cooldown in the druid toolbox, keeping them (more than) afloat, the priest lacks a mid-cost spell that covers regular healing. I really hoped that Greater Heal would be that spell in cataclysm, but it is just too expensive to use non-stop, and the HPS difference from Flash Heal is very very small.
Disc is a bt of a hybrid, getting the best of both the druid and the holypriest. Borrowed Time, Power Infusion and penance gives the discpriest a very strong toolbox for overdrive healing (none of which you added in your calculations above, zakaluka). On the other hand, the discpriest really need this toolbox due to all priest base heals being rather weak. The HPS may be good, but the throughput from individual spells often leave something to be desired. The crit buff in 4.2 changed some of this, but still. We're not exactly shammies or paladins here.
Either way, I believe that Holypriests need more mana regen to be truly competitive in single target healing. That is at least my personal opinion. There is nothing wrong with the throughput, and if the tank is overgeared we can always hold back enough so that it is not a major issue. But when facing a bad group with a bad tank, the holypriest is simply powerless. The much required overdrive button simply runs out halfway into the fight.