They're both dps jobs that play reactive to procs, maintain a buff, maintain a debuff, and really not much else differentiation beyond that. When you compare BLM and SMN, they have umbral/astral and aetherflow/aethertrail respectively; both persisting mechanics unique to the job and their base rotation. The most you can get out of BRD/MCH is ammunition, which is practically another oGCD that gets used up without a thought and as soon as it comes up because it's free damage and tp, especially since only two skills that MCH use actually get any additional effect from ammo that isn't the base 20 potency. There's very little turret interaction that it becomes an afterthought until you need to use regen or hypercharge (which is a cooldown and isn't necessarily part of their main gameplay, or is "part of it" as much as ninja poison and FoF is to monk). Of course it also doesn't help that GB/WM are functionally the exact, same abilties, alongside other carbon copies like quick notch/spread shot and Wide volley/Grenado (both of which could've been opted out for an AoE attachment or something)
Even if you were to go by their movement, that shouldn't be their only differentiation. I won't argue that MCH is more motile than BRD, but I don't move that much to begin with unless mechanics call for it anyway, so it becomes less of a defining trait.
I also don't understand why people refer to "banking ogcds" to have abilities to use when they can't stand still...because those oGCDs are going to be used when it comes off cooldown anyway and aren't on the GCD timer.
Having played both jobs, leveling both casters and a DRG, as well as and being anxious about MCH being a new job, the best way I can sum it up is that I'm disappointed that this is the final version of MCH that we got (especially in relation to BRD and how they got slapped with wm) compared to what they had initially previewed with ammunition usage and various attachments.