Note that it's also a 2nd level spell, where
divine favor is 1st level. That probably explains the difference in the maximum allowed bonus. (Well, that and also that it only affects animals.)
Incidentally, it is my opinion that virtually any spell that has a casting time of a Swift or Immediate action is questionable at best - that's the equivalent of having the Quicken Spell feat applied, which means that the other effects should be roughly equivalent to a spell four levels lower (which is never the case). But that's just my opinion, and not really related to RAW in any way.