I very deliberately chose the champions I chose, they are all currently top tier, or nearly top tier.
To be clear, it's not just a slow, its a movespeed steal. this means that though the slow is small, it functions a lot better. it also can functions as a ranged ping, finishing off low health targets that are too far for you to engage on, something red smite can't do at all.
and also, unlike red smite, blue smite retains usefulness in teamfight, red smite is entirely useless if there is more than one target fighting you, as the target you smited can simply disengage while another target murders you, where blue smite would give you reliable damage and cc. which you could use to disengage yourself.
Infact, blue smite functions as a counter to red smite. in a mirror, two champions with smite and the same kit, the blue smiter would have the advantage in a duel, first by both blowing smite, and blue gaining distance, and escaping the damage of red smite, thus gaining essentially free damage, which then puts blue at a slight advantage.
Red smite is the inferior smite in every regard, with the only champions using it being the ones that either can't use blue smite effectively like nidalee, or the ones that have particular synergy with red smite like kindred.
and even in cases of the latter, blue smite is still an acceptable decision, as it is a better smite.
you shouldn't argue this anyway, you seem to be a support main, not a jungle main. you don't know, you just see trends and think it means more than it means. the fact that voli uses blue and not red should be an indication to you the blue is stronger, as voli could use either to an equal effect.