That's not entirely true. Let's say you only get 5 casts of Solace a minute instead of 6. Now your regen is 5*2.8+8 = 22% regen per minute. 4 Solaces = 19.2% regen. So you could in fact wait five seconds after it's off cooldown and still get more regen than with Mindbender.
It does require more effort and awareness than the Mindbender which is pretty much fire and forget, but you certainly don't have to worry about casting it within 1 second or it's a regen loss.
Of course there is an argument as to whether the heal from Solace is worth it in which case is it really regen if the mana spent gains nothing, and if you have significant disconnect time (Garrosh Intermission phases, Immerseus submerges, if you're assigned to towers on Galakron etc). then it reduces the effectiveness. But it still looks better on paper...