I don't think you understand how tiers work. OU and BL are considered around the same strength.
This statement in itself is wrong, unless we have different definitions of "strength". Heracross possesses the same strength as Pinsir? Infernape is as strong as Blaziken? Flygon compares to Garchomp?
While there is no fixed BL metagame, the BL Tier can be divided into two categories : Those pokemon who are just barely too strong for UU, thus making it an UU banlist, and those who are clearly too strong for UU but just short of achieving OU
power. This in itself is the reason for the huge discrepancies existing in the BL Tier.
Also, there is a correlation between usage and power. The strongest Pokemon will always end up being the most used because competitive players naturally select the stronger Pokemon for their teams. Suggesting something is used often and weak is clearly wrong. :/
While there's no arguing with the logic of your first sentences there, the bolded one I disagree with - something can be used fairly often and be relatively weak.
Incidentally, Jolteon appears as 38th on the weighted usage statistics for the sole reason that it makes a decent lead and an alternative to the 10 completely broken leads in the metagame - it simply is too weak to play any other role well, and EVEN in the "lead pokemon" department (it's speciality, so to speak), it is outclassed by at least a dozen other pokemon.
Also, by definition, Deoxys-E and Wobbuffet came down from a superior metagame, Ubers, so you'd think they'd be in the top 10 most used pokemon right away - they make a measly 45th and 47th. Snorlax is 21st.
Suggesting Jolteon is to be moved down to BL when our algorithm suggests it is used enough to be considered OU is kinda... well, dumb. Same goes for Weezing. He isn't USED enough to be considered overUSED.
The difference being that in terms of STRENGTH, Weezing's typing, ability and stats make it unique and not directly outclassed by any other OU pokemon - while Jolteon has the ability to a) batton pass substitutes or speed or b) fire off hidden powers and her 2 other special moves - she is outclassed in both roles by other OU pokemon (Ninjask and any top special sweeper, respectively).
As you say, generally there is a correlation between usage and power, but there are exceptions. Dragonite, for instance, has some incredibly powerful options available to it, yet it just barely makes OU nowadays in terms of usage - because it is totally outclassed by 2 superior (more powerful) pokemon.