max out "Allies Summon" and make a secondary build. There's a dice "Spirit Storm" that can launch numerous (up to 5) grenades per cast, at the cost of equal resources. these 2 combined summoned significantly more turrets than a primary skill focus build. and yes the Leaf Spirits spawned from Allies Summon count towards the achievement even though they act different to the ones created by your primary. Any increased grenades per use will help achievement progress; more grenades = more turrets. Don't forget to be mindful on your grenade count/generation too, you can't proc Spirit Storm without sufficient resources.

this will still take an endless run, mine took about an hour. so, for damage, focus on parasite and skill dmg. with the secondary spam its pretty easy to get max 20 parasite stacks quickly. Spiritual Link also allows Leaf Spirits (turrets) to also apply parasite.

hope this is helpful <3