Wow, Mother Brain is a beast. Does she have the most HP of any boss in any 2D metroid? Id think Metroid Queen has a lot but probably not that much. I guess youd have to compare Mother Brain's 2nd form and discard the 1st & 3rd when comparing to others since they are special circumstances.
MB second form takes 30 more regular missiles than MQ does (even though she's killed by like 4 bombs in the stomach), but MB2 doesn't seem so bad because you have super missiles. Also, the strongest beam combination is 9x as strong as missiles in SM. I completely forget SA-X's and OM's health, but the beams in Fusion are so hella strong that it doesn't even matter.
These are all off the top of my head, though, but I think it's right.
These are all off the top of my head, though, but I think it's right.