Except the difference between a 2 seal and a 3 seal Divination is 1%, is it a difference? Sure, but not enough that it's a massive loss if you get unlucky with the seals. So while yes ofc you want to optimize and get 3 seals, it's not the end of the world if you pop a 5% with your groups raid cooldowns.

Infact, in your opener it's more important to get Divination out within the 4th or 5th gcd to align it with raid buffs then it is to get a 3 seal divination.