Summoning is good because its effect isn't permanent, like Chaos, meaning the spell lasts for a long time. Summon Fire Elementals and a Phoenix, and then cast Darkness spells calmly – slowing, weakening... Or start with slowing, then focus on summoning, and then back to Darkness – it depends on the situation. And higher-level Darkness spells work very well with Summoning. A Phoenix with Vampirism and Celestial Shield, along with the Warlock's Spell Penetration, is practically invincible.
In terms of creep clearing, I prefer Summoning over Chaos. The AI is terribly slow when dealing with summoned creatures. You can take Utopia very early using the Wall of Swords, which will allow you to significantly outpace your opponent in development. And in general, large creatures can easily break through the Wall with Furies.
Unstoppable, by the way, isn't discarded even when using Summoning – because it also includes offensive spells. In particular, Unstoppable allows you to cast Hornet Swarm even on undead and golems. Also, mines work on everyone, bypassing resistances and immunities.
In general, I recommend giving it a try :)
Горящие реки сходили с ума, пытаясь остаться водой,
Земля пропустила коварный удар, раскрывшись на шаге вперёд,
Взлетел разъярённым драконом Огонь и понял, что тоже умрёт...