my argument is based on:
Faster manual speed exist for every race/class combination and doesn't discriminate against you even if you have or don't have feats rapid reload/rapid shot which both make shooting faster. (repeater isn't really a repeater without weapon prof so i assume that weapon users do have the required feat if not.. keep your delay)
The delay exist from lammania pre-U11 where arties were put in where in first version it was *majorly* broken. well, whole repeater speed was. manual attacks had like 50 to 80% increase compared to holding button down. up to and and over 180 bolts/minute with no regard for BAB or anything. clicking meant never ending machinegun whose maximum speed was attainable at level 1.
so.. yes, it was broken. it was fixed to follow BAB as it should but they either didn't notice (how couldn't they, it's clearly visible if you shoot more than two times in a row) or didn't care about the delay after reload animation that exists after each shoot-reload loop.
at same time they also changed old click for each bolt, reload way that repeaters worked (since it caused "missing bolts" that never appeared) and for some reason, that "small" delay was left in.
funny fact is though that old missing bolts bug gave pretty much same amount of bolts that HIT your target as this "new" version that slows down your attack speed if button is kept pressed down.
so.. current bug is more reliable since it works same way 100% of time than the old bug where sometimes you lost 1 bolt, sometimes 2 but in the end, you get pretty much same final count.
Turbine, making bugs more reliable since U11 :P