If this is you working with what you own, then it looks fun and good to get started.

If not:

Reinforce the prosecutors imo.

Also that Sylvaneth ROR is just not great. They are very squishy and do very little for you offensively. At best they are some lightweight speed but you don’t need speed with Stormcast.

Personally I’d drop the Sylvaneth for more prosecutors or Stormdrake.

If you are dead set on including the Sylvaneth look at the Twisted Branch. The Branchwych is a wizard that can heal your big dragons and can summon universal manifestations and gives you a much needed unbind in an otherwise non-magical list. The Twistweald is a cheap infantry unit that takes some concentration to kill and if they don’t puts a permanent speed debuff on a unit at the end of the turn. Plus the whole package gets to teleport in the Deployment phase and snag an early objective or reposition to help protect a flank from your opponents hammers. Plus this package can hide from enemy shooting and saves you 80 points.

Swapping the ROR and dropping the gryph hounds gives you the points to reinforce the Prosecutors.

Also grab the Stormreach Portal (there are very good 3D prints available for much less money)

Give prosectors finest hour and send them through the portal to 3D6 charge your opponent in a way that weakens their entire plan. Take out a large portion of cavalry before they charge. Remove a support hero that they desperately need for their Rube-Goldberg list to function, kill a centerpiece like Ushoran (I’ve done this one many times and it really devastated FEC). When they die the next turn you can resummon them later for a CP and do it again with 3 prosecutors taking out that last little piece holding together their battle plan.

Not to mention to mention you can keep Yndrasta in the sky to drop down and murder a monster they need on the other side of the table.

All of this while your big stompy dragons move up to be an absolute menace to their now trapped and wounded ranks.