The RNG grind for substats isn't nearly as bad as other Relic rng steps, and has potential to get up to 1k total substats, which if you're really lucky can get a substat with all 1k points in it. Two of the NMs can give you a full bar of light, and a good light party can get you more light than you know what to do with with it only taking 2 crystals (light bars) per roll.

Also you'll be able to roll your stats again in Hydatos, so even if you don't get stats you like in Pyros you will be able to keep rolling in next Eureka zone.