Prophet's heals are exactly as efficient as a bishop's. The only difference is that a bishop heals for more at any one time.
Good thing you didn't flame, because flaming someone when you're the one who's wrong usually gets really embarassing really quickly.
I think the order SE > EE > PP > Bishop is pretty much correct in terms of duoing partner - recharge with HMG is not to be underestimated.
Prophet's highest level heal costs 52 MP and heals for 301 HP. The amount healed by a non-bsps heal is the square root of your matk+the skill power, meaning a prophet with 500 matk will normal heal a player for 22+301 HP, or 323. This is 6.21 HP per mp expended.
A level 56 bishop's heal has a heal power of 633 and costs 90 MP. Adding in a 500 matk of +22 hp healed, this is a total of 655 HP healed by a level 56 bishop not using bsps. This is 7 HP per mp expended.
A level 74 bishop's maxed heal is 858 power for 120 mp. Again, the square root of your matk is added to the heal. With 500 matk, the heal would be 880, or 7.333 HP per mp expended. With higher matk like a level 74 bishop or prophet would have, the efficiency begins to stack in favor of the prophet's heal (but a bishop's non bsps heal is still more cost effective by a ~little~ bit.
A bsps heal is more complicated. The max bsps effect requires what seems to be an equivalent matk to your skill power. A prophet's heal only needs 323 matk to achieve the maximum boost of a bsps'd heal. A bishop requires much more than that - for a level 74 bishop, they need 858 or possibly even more matk in order to obtain the max bsps effect. The bsps effect, when maxed, provides a very noticeably better heal. If the matk does not meet the requirement, the heal isn't boosted by nearly so much.
It's true that a bishop's heals are slightly more efficient per mp expended. It is not true that a bishop's heals are extraordinarily more efficient than a prophet's heals. They heal more per cast, but the efficiency is nearly the same.
Now look at the context in which we are speaking. We are looking at a SH who is going to duo with a prophet or a bishop. The prophet sports acu 3 and zerk 2 while the bishop only has lvl 2 and 1 respectively. This means the SH can cast body to mind sooner with the prophet's buffs and can do slightly more damage because of zerk 2. The SH is able to restores its own mp faster because of the prophet, and the prophet's heals are nearly as efficient as the bishop's.
So a prophet's heals are on a different scale than a bishop's, but they are still so similar you may as well call them the same.
Since we aren't arguing over EE, I won't do it but an EE is much more efficient than either a prophet or a bishop.
Edit:I forgot to add something else. In the context of this, a prophet will not run out of mp buffing and healing a SH. Therefore, the question isn't efficiency in the first place - both characters are able to keep a SH's HP topped up without ever running out. In that sense, the efficiency of both are 100% in terms of heals, which means that they are exactly the same.