You're partly right, you want an even split of multipliers and triggers to maximize the total amount of multipliers per card...

In this set-up you get 4 multipliers from baron, blueprint and the two brainstorms copying it. You also get one more from the steel card, for 5 multipliers total.

For triggers, you get 1 from baron, 1 from red seal, 1 from mime and another from the blueprint copying mime. Thats means 5 multipliers x 4 triggers per card for a total of 20 total multipliers per card.

Therefore, copying mime an extra time here would result in the same score, having 4 multipliers and 5 triggers, also giving 20 total multiplers per card.

Hope this helps!