I think SpaceHam means swapping it for magic domain clerics only.
This, however, sort of undercuts his argument:
all the other features of the Magic Domain are great and handy (extended melf's? hell yeah! acid dmg for days n days)
If the domain is already strong, then strengthening it further would tend toward making it unbalanced.
For example, see the Evil Domain, which gets only 3 spells, as opposed to five for the Magic Domain, and one of those spells is also Negative Energy Burst. One of the two other spells, Negative Energy Ray, all clerics get, only at one level higher.
(The Evil Domain does get the power to turn Outsiders like undead, but I bet that's not very useful in POTM.)