A Spellsinger has the option to be a good CC and also a good healer, no one I read here said it is different but this means not that they should not have the option to be good sonic spell casters if one (even if not you) prefers this play style.
And just to mention it, a reduction of cooldown and an AP points reduction is for sure not only a quality of life improvement it actually buffs you CC power and frees APs for other enhancements (also most likely more power).
But I agree that Mass Hold Monster cooldown is too long and I would not complain if the bard would simply get the wizard version of this spell in the spellbook instead of an SLA.