I would sure be surprise facing it, cause I never saw any on Div 1.
It's sure not about power, but DPS, what sure minions don't have. Summon Haste isn't even viable on arena, since it becomes only 4.8% on level 20. As your minions die, your DPS goes down, so it's very probably your average DPS is very low.
There is no comparison between an Immortal Build and a Summoner Build: Skullshield implies in 30% DMG reduction with no extra costs, while with Spirit Master (4) + Summoner + Divergence (4) you have only you have only 18.4% DMG reduction. Also, unlike Immortal Builds, Summoner Builds would just worst with draws, in the sense at some point they would instadie by a simple charge. About their power, you're definitely missing Skill's Damage: Whirlwind has 500% MH, Scalp has 400% and there is 3x 300% of Skullshield, which together have ~76% more damage (figure out how many Barbarian, PTL and Summon DMG to reach such multiplicator) than five minions + taunt minion (which costs 2 Set Affix Slots), not even mentioning their far greater APS. This can be a little better with Apocallypse mythic, but I also didn't consider they don't have a weapon mythic to answer back.
The best choice for a Summoner Build would they as a "Suicide Squad", which walk to your opponent then explodes in his face. Patch 3.0 even helped this idea: +40% Damage from Sacrifice  (It was only 10% before it) and Sadism will boost a lot such build. Albeit if you look properly, this is just another projectile build: You have slow auto-aimed projectiles, which most probably are outpowered by any other wizard choice.