Increased minion size should also come with increased AOE

Exactly. You only have access to 5 mages with a relatively huge invest into the passive tree and a special node in the skilltree. If you decide to go Archmage, you don’t need those nodes because you don’t benefit from them. You can spend them elsewhere.

Also the frostbolts from Archmage can Shotgun.

You could go for a Hungering Souls build with utilising the “X% more damage with exactly 3 Minions” with an Archmage and Twin Golem.

Yes. So if you have a max of 7 and take phalanx, you get 4 × 180 = 720 > 7 × 100 = 700

So it is situational. You have to invest to get additional summons, be it skeletons or mages. All I mean is that there are situations where you have a benefit from that nodes.

I don’t say that these nodes are great in all situations. Just responding to your general statement that these nodes are “utterly garbage and decrease your DPS”.

I personally would not want to change these nodes very much. Because if you buff them to be of an advantage over more minions in general, you just gimp the skilltree. Everybody would choose these nodes. It would just switch the actual situation into the opposite.

I’d prefer some build options in the passive tree for single minion (or low number) builds. Similar to the Beastmaster. Give the Summoner some defensive bonuses the less minions he has active.

Something like this.