My guess is that when they started designing MCH, they decided one of their rules for physical ranged DPS is that it had to be like BRD in a way. Serving a similar purpose while having the same/similar utility (meaning instead of competing for DPS slots with BLM, SMN, DRG, NIN and MNK, MCH is only competing with BRD). Of course, this also trickles into it having similar gameplay; a problem made worse by using the same mechanics in the post-50 game for both jobs.
Back in ARR's beta they talked about the fact that combos as known by melee don't really fit a ranged class like archer/BRD, which is why they went with procs. I originally figured that for the sake of making the jobs different gameplay-wise, they'd design MCH with weaker attacks that are instant and heavier attacks with cast times, and perhaps interactions between shots (basically the idea behind Wildfire but expanded). Hence why I'm of the belief Gauss Barrel and Wanderer's Minuet shouldn't exist, yet they do because this is the gimmick through which you see changes in gameplay (I'm guessing to match up to the new systems added for MNK, DRG and SMN, though those systems added to gameplay rather than take away).