Since its a pure damage trait, its not really improving an heralds/boonbots overall dps.
Draconic echo is in every way improving the overall dps. Shiros F2 is almost the same in raids as forceful persistence.
And compared to fights outside of 10man groups, (where fights go longer than.... one shots?)
its still less damage than Draconic Echo
Why? because Drac. Echo lets the herald keep up 25might permanent through Incensed Response. So in longer fights its an better choice than forceful persistence.
(not to mention the boons that you+9allies that are being kept up, like swiftness or protection - btw having no boons for some time means less dmg ...~1% less per)
My opinion: The support side - herald with its aspects - can stay in his damage he gets now.
Other upkeeps - like legends that dont rely on buffs like herald (shiro/mallyx/dwarf) - should get an way higher dmg boost out of that.