Except you can't be... You just cast Conjure Animals and are concentrating on it. Invisibility breaks if you cast another spell AND requires concentration.
Or are you saying your build relies on ANOTHER caster maintaining concentration on Greater Invisibility for you?
I feel like you're not debating in good faith here.
Edit: Also there is no first level spell that shuts down fireball. Absorb Elements will let you reduce damage, but I only need to deal a single damage to trigger a concentration check.