We tried a heal party spammer during the factions preview in 12v12. It's not effective at all. Heal Party
does have a range, and the 12v12 maps are quite huge. If your team was playing 12v12 right, which more and more teams will start to do as time progresses, they would be split up into small groups of four or less, going around capturing/recapturing flag points.
From what I saw in the FPE, the game usually consisted of a group of 8 players running around in a pile killing everything in their wake, and then a group of people that knew what they were supposed to be doing and were running around checking on flag points and trying to capture enemy flag points.
The only time that it would be ok for the whole team to be standing around near eachother, where Heal Party would actually be effective, would be when they control all/most of the flag points and are waiting for the game to end.
Of course the tide can turn easily if a team doesn't know what they are doing. I've seen a battle where my Luxons ran in and pwned all things, captured most of the flag points, and then stuck together camping the dragon roost (the dragon roost isn't as important as you think) while the Kurzicks managed to recapture all of the outside points and win because they had more captured points, and my silly Luxon team was too stupid to help me recapture them
Having 2-3 monks that go around healing the seperate groups can be effective, though not actually neccesary, but Heal Party definintely isn't worth it in an Alliance Battle.
As far as MMs go, they were quite effective at the beginning of the FPE, but then ppl started getting smart. Some ppl brought Verata's Aura to pwn the Minions onto their side, but then near the end, when more people started to figure out they should be split up, the MM became very unaffective. The more teams learn to fan out and cover ground, the less effective the MMs will become. There will be less bodies nearby them that they can use, and it will also be difficult keeping the MMs alive for very long while transporting them across such huge maps.