IMO, it depends on what kind of spellsinger you are. I do Primal Avatar / Strike a Chord on my Stormsinger, and I know a guy who does E.A. because he's doing the Bard healer thing.
The reason I like Primal Avatar for the mantle isn't just the damage proc: Evergreen allows you to turn on Max/Emp/Quicken/Intensify, skip metamagic reducers, and forget about mana management. Shared Mantle works amazingly well for allowing my Oozy minions to tank stuff for me. And, specifically for a spellsinger, I have 3 different proc timers for my main 3 elements.
Also, just for clarification, you feel that Echoes of Discord has a slow cooldown, yes? (Because, that is accurate!

) I don't think there's an Epic Strike cooldown faster than Strike a Chord. Strike a Chord stands out when you pick up Master the Acoustics.
Some other options you might want to look at:
- While I'm not a fan of Machrotechnic's epic strike for a caster bard, I do like Thunder Hammer as a bonus SLA. Also, you can pair Blast Shields from Machrotechnic with Natural Evasion from PA.
- Blue Draconic Incarnation would probably be pretty great on a Chaosmancer (The Iconic race) based Bard, since you have access to Lightning stripping. Also, it's an excellent 3rd tree on a Stormsinger for the Scales of the Dragon and Elemental Blood abilities.