Most level 1 focus spells tend to be weaker than normal 1st-level spells, but I was looking at the Sun Domain's Dazzling Flash, and it looks legitimately on-par with 1st level spells. Compare it to Color Spray, which is quite similar to it, and in most cases, both spells will achieve the same effect. Not only that but Color Spray is already a really good spell, so getting that on a focus spell is a great pickup.
The thing that really made me go wow about Dazzling Flash, however, was the part where its area increases to a 30-foot cone! I would legitimately take this spell on my Wizard and cast it with 3rd-level spell slots if I could! And getting it back with just a 10-minute rest!? That's nuts! For the power this spell has, I'd expect it to unlock at level 8, but it comes at 1st level!
What's more is the multiclassing potential. I legitimately think this one focus spell is 100% worth two feats, no questions asked. Not only is it probably the best 1st-level focus spell, but it gives you an extra focus point for taking it!
"...in most cases, both spells will achieve the same effect."
Stunned 1 & Blinded for a round is worse than rubbing one's eyes for an action to lose blindness (which is comparable to Stunned 1 alone).
Lose action (whether or not blinding bothers you), be blind for other two actions, then dazzled afterward.
Use action (if blinding bothers you), dazzled afterward.
To pass the time in an easy battle without using too many resources, sure, it's a nice spell.
Whether Dazzling Flash dominates other focus spells is another issue. I'm partial to the 1-action or Reaction spells, as you might actually use those in tough battles.
It's a nice debuff with the potential to hit quite a few enemies.
Color Spray is stronger, but needs to be cast from one of your top level spell slots to keep up (due to the incapacitate trait). This is a big downside, but also allows you to easily upgrade to more potent spells like Vibrant Pattern at higher levels.
Dazzling Flash has a material component and requires a free hand (or one holding a holy symbol or emblazoned weapon/shield). That's quite easy to achieve, but somethign to keep in mind.
It is definitely one of the more power- and useful domain powers. And it gets bonus points since its follow up ability isn't too bad either.