Yeah it makes a lot of sense at 3N per casting, though the vast majority of the forms, I still feel are wholly unsuited to combat use.
Out of 25 mages (2 died the last turn to Mind Burns, can't remember what they were, but I think they can safely be classified as "MR too low to survive combat" -
3 Foulspawn = 8MR
2 Dragonflies = 3MR
12 various animals = 5MR
1 Winged Monkey (so cool!) = 7MR
1 Bog Beast = 7MR
2 Ice Drakes = 9MR
1 "Hydra Hatchling" (looks like a mature Hydra missing some heads, only 1 form) = 12MR
1 Wyvern = 12MR
1 Chimera = 13MR
1 Amphiptere = 16MR
So if I count the 2 that just died, I had 20% Feebleminded (the Foulspawn and Dragonflies, who are actually at 3MR and -2MR atm from Affliction), and 16% who have >10MR before items. Of those 4, none of them have anything but misc slots, so besides the kind of awesome Amphiptere, none will surpass an unbuffed Capricorn, even with an Antimagic Ammy. (on the bright side, 25 ex-Capricorns with 1 star, and in 1Magic dominion will net you 250RP for free, and cut upkeep by ~583g)
As far as Mermages as support mages..... they are almost identical to a Capricorn out of the water. Without going into length, I'll just say that I didn't think I was the only one that felt that it wasn't just that Capricorns were too expensive once removed from the water, but that their paths just sucked in combat by that point anyways. Not to say that some Mermages wouldn't come in handy, but there is little good they can do that won't have them passed out by round 5, and not much they can do before that.
So, trying to look for an angle that allows land to be conquered early on, and Conj to be researched early enough to not only get a good stable of summoned mages up very early, but to make them visible to your neighbors, so they understand the risks involved in trying to marginalize your holdings. All this is a very tough task to accomplish, when it's well known that you won't get better than N2 or W2 for combat magic without your pretender, or summons (or booster items, but Water is way out of early reach, and Nature seems a very poor use for your gems, considering your other goals).