I don't know, for example Mythic Charge is basically once per combat. Leading strike is one attack per turn. Thundering strike is usually once per turn but sometimes it is not. Also some enemies are resistant to Sonic
To me it sounds like Elemental Barrage now only gets proc'd by Spells with Elemental damage, so it's now sort of a Caster-exclusive Ability. Casters have way better shit to spend their Mythic picks on, like Abundant Casting, Favorite Metamagic, Impossible Domain, Ascendant Element, or even things like Archmage Armor and Enduring Spells if you wanna go a little wild etc.
You get 10 picks split between Mythic Abilities and Feats, and I don't see any scenario in which this version of Elemental Barrage warrants a place among those 10 picks compared to other choices for Casters.