A few things I've noticed in a Nightmare run-through with Antimagic/PES/Superpower here
(having some trouble with my pre-Steam login on Steam so started a new account to try Summoner again). These may already be common knowledge, but given that this is the most up-to-date Summoner guide and the guide notes that Antimagic may be worth it, it seems worth mentioning them here.
1. Antimagic Shield is running around 123 points absorbed while walking around normally and 71 retaliation damage, up to 150 absorbed/89 retaliation with full PES - Heroism - Lightning Catcher (managed 11 stacks, not sure how, may be an artifact of Grand Arrival with Drake) - Militant Mind.
2. Resolve can crit, which means that while the talent description says it adds 52% in practice it's often adding between 70-80% resistance, or, practically speaking, whatever your cap is.
3. Resolve's % reduction happens before Antimagic Shield's flat reduction.
4. With Resolve 5, equilibrium regenerates while standing in Devouring Flame, while Rimebark's Winter's Fury breaks even on equilibrium.
5. With 100% Freeze/Stun immunity and Antimagic, you can stand in the overlapping Winter's Furies from Rimebark -> Frantic Summoning -> Rimebark without any real effect (note that they will kill each other, though, so you have to space them out a bit). You'll take the first hit for about 40-50 damage to activate resolve, then Resolve kicks in and you don't take any more damage.
6. You can end up brainlocking your own minions with Aura of Silence - not that bad with anyone but Rimebark. The equilibrium recovered is pretty solid if you ever need it.
Also worth noting that the most recent patch made the drake hatchlings not count against your limit, so I don't think there's a reason not to max out Grand Arrival. Sometimes the battlefield can get pretty congested, and the modest range on summons means that reaching an extra space with those damage resist debuffs can be pretty useful.
1. It's a nice amount of absorption, but it might seriously not be worth losing arcane gear and runes
2. Max resist can easily be reached with an endgame wild or defensive phase door either way
3. This is nice, but keep in mind the most dangerous times magic happen it's big amounts of spike damage which antimagic may or may not really help with
4. This is also nice, but you're spending 5 points in something that you can otherwise do just fine with jelly and 1 point in nature's equilibrium
5. I never saw any reason whatsoever to stand in the rimebark aoe myself as there's no reason to and some positioning gets rid of the problem entirely; I still want rimebarks to hurt jellies on occasion if the battle is too dangerous
6. Silence is nice but it can be easily gotten through itemization, like torques
Not maxing grand arrival never had anything to do with drake hatchlings, but a little more range might just not be worth it depending on your point spread, it's not a big enough advantage to justify 2 class points.
Basically there's a few nice little tricks you can reach with antimagic but like I said it's heavily up to the player and I don't think it entirely justifies itself for summoner, might make low level play easier overall though. I might just be biased against AM after it being mediocre for so long, will have to give it another try soon