Really, one of the things that needs pinning down is just how much exactly does INT and secondary stats impact things.
Since, while BLU gets bonus magical power from INT, a BLM has not only the stats on their weapon (Both INT and some secondary stats) but also has Enhanced Intellect traits for bonus INT.
Then of course, there's Maim and Might vs Magick and Might 50% vs 30% with also Off-Guard vs Astral Fire 50% vs 80%
Essentially, potency wise, BLM has Fire which is 180 and then it's amp'd by 110% by M&M and AF up to 378 potency. They also have procs of Fire III which is 240 and then amp'd up to 504 potency. Meaning that on average they push out 428 potency with their Astral Fire CD's (Assuming perfect 40% of Fire I replaced with Fire III)
BLU has Glower (Or another of like a million other spells) with 130 potency. Amp'd by M&M up to 195 and amp'd by OG up to 293 potency.
If you then account for their oGCD primal skills, they get 220 from Eruption (495 after amplification) for ~41 potency per GCD, Static Strike for 310 potency (~678 after amplification) for ~29 potency per GCD and Glass Dance for 290 potency (~653 after amplification) for ~18 potency per GCD.
Putting BLU's average potency per GCD to 381. With Peculiar Light averaging about 26 potency per GCD bringing that up to 407 potency per GCD.
A mere 21 potency per GCD away from BLM. Which may or may not be matched by Torment vs Thunder it's harder to average them out because of Thundercloud procs being weird and dealing full damage of the DoT in addition to its refresh... Potentially doubling the output of the GCD spent refreshing it.
At the very least, the time that BLM has to spend in Astral Ice would put the 2 closer to each other in terms of potency output.
So again, it really hinges on just how effective BLU's INT scaling is at matching the weapon damage, INT and secondary stats that BLM has from their weapon and Enhanced Intelligence traits.