I'm not sure what damage type of damage Grasping Vine actually does, but since it does consistent damage so I think we can safely say that it's not fire/electric/death/cold. Maybe non-elemental, yeah, would make more sense.
The magus build (and any build which invests heavily in +% power recharge I guess) has amazing power recharge rate. This is in part because of bonuses from various unique items and the recharge wrath (or the Lap Dragon, if you have one - I prefer Lap Dragon + Earthen Embrace setup, since I usually don't bring a shielder). You can literally just count 1-2-3 and then *power recharged boom sound* - and this is with a "normal recharge" power. I think Arcane Orb is crucial because it's essentially free damage - use it, and you're ready to use a new power long before its duration runs out. If you have the Power Recharge Chant then all the better. That means you can spam Invincibility too.
He's not particularly noteworthy until higher levels though, he usually starts to shine around the time you start getting the Circle of Four set. Before that, he's more like a versatile mage.
For end game, I also aim for uniques and I always try to find a staff/amulet/spellbook with +4 to the Lightning skills (combat) and +4 to the Summoning skills (nature). Such items doe exist, and I've managed to find at least one in all my games with a Magus. Granted, I normally don't visit stores that much unless it's for this character.
Aiming with Aether Blast is easy if you have curses like Drown, and Blast's AoE is great at level 3. Ranged mobs are tricky and I use Ravaging Strike/Thunderous Shot/Flurry for those, but against melee mobs it's just a matter of cursing them (drawing aggro), running to your summoned minion, waiting for enemy mobs to catch up and then using Blast. A little extra work = cleared screen. Almost like World of Warcraft again, heh. Works like a charm even in Elite, though you need to be careful and make sure your mage doesn't take too much damage. It's true that for some reason Aether Blast does horrible damage against certain mobs though, and I have no idea why that is.
My summoned minion remains tough, but I think this mostly because I invest heavily in the summon line (via items, power requirements). Note that there are different types of summons, and each one has a specialty. Like the Ketril has the highest armor but the lowest DPS, while the Lertisk has the highest DPS but the lowest armor. I usually switch to the Ketril and sometimes the Forest Golem at higher levels. Party buffs also help - Earthen Embrace, in particular, increases your summoned minion's maximum HP resulting in a dramatic increase in Aether Blast's damage (around 6k+ in elite difficulty, depending on factors like Enveloping Embrace and +%power damage mods - because of the way things are calculated, any +%power damage mods will actually give you higher returns if the minion is buffed with Earthen Embrace. This is because, technically, Earthen Embrace doesn't count as a +%power damage modifier - this little loophole is the reason why Aether Blast can do as much as 40k damage on normal mobs with minimum preparation. Could be much higher if you go nuts with the science I guess, but I'm not really sure how high it goes since I only play long enough to finish all primary quests).
Anyway my summoned minion usually doesn't get swarmed thanks to curses and the party ranger, who seems to have an uncanny ability to draw aggro. The real danger is if my mage takes too much damage and the minion dies because of Summon Bond before I can cast Aether Blast. Luckily there's panic button: Invincibility.
I prefer Aether Blast to Corrosive Eruption for general AoE, but I can't say I've ever been forced to choose between the two. Someone always has at least level 1 Eruption in my party, because it is a good power and costs only a single skill point.
Intelligence is very important for the magus being a multiclass, as I said, because a large chunk of your damage still comes from spells. Sure it's easy to max INT if you're a pure combat mage or nature mage, but the reason why certain combinations like melee/range don't really work (or are very difficult to level properly) is because a melee/range character would need high STR and DEX to do high damage. With a magus, it's simple - since you keep casting spells, your INT increases naturally. This is why I think the magus (or combat magic/nature magic) is DS2's "hidden" multiclass. It just works well, and it's been there since before Broken World.
Edit: Figured out why Aether Blast's damage seemed so inconsistent - it does DEATH damage. Grim Necromancy does not affect it, but Infect and death resistances or immunity do. On my current run I'm doing 30k+ Aether Blasts (with Lap Dragon Power) in Veteran with a level 55 Archmagus because of Infect, on creatures with no death resist.