Currently the Mossie is a rather weak attacker {the guns are murder though!}, though I occasionaly fly it I still am holding out for the bomber version with increased payload/speed at altitude.
It's not the Mossie is weak, but rather some fighter/bombers (mostly AAC types) in the game typically carry a lot more ordnance than it usually would. For instance, IIRC the 1k GP bombs themselves were pretty rare in usage as compared to the more common 500lbs bombs, not to mention some planes like the P-38L would usually made it a habit to take off with lightened fuel loads when they would actually strap themselves with so many bombs and rockets.
Imagine what the MA'd be like if 1k bombs were taken out of the game, or perked at a reasonable price to keep it rare. If most fighter/bombers are limited to 500lbs bombs, you'd soon realize that many of the 'attacker' planes we have in the game actually carry a significantly heavier load for the jabo load.
However, as it is, we've got late-war US fighter/bombers that carry some 3,000~4,000 lbs worth of bombs and rockets, free of charge. These fighter/bombers not only carry much heavier loads than some of the specialized attacker planes (such as the A-20 or the Mossie), but it also functions as a normal fighter aircraft after the bombs are dumped.
According to my analysis, this is actually one of the reasons of frequent phenomena in the MA known as 'suicidal jabos'. Basically, if something like a P-51D or a P-47 or a Typhoon comes in with alt, it is basically uninterceptable. People could just slam full throttle and angle themselves straight to the target field, and nothing can stop them in time before they dump their payload. I mean, whose gonna catch up with a P-47 or a P-51 in a dive? Even with the added drag of the bombs and rockets they're still faster than most planes in a dive.
IMO, the heaviest of ordnance options should be perked, so most fighters are usually limited to one or two 500lbs bombs max, and only the attacker lanes may carry much heavier loads for free. If that be the case, then the planes like Mossies, 110s, or A-20s would be considered a very significant attacker plane in the game, not to mention reduce the overall effectiveness of suicidal attack runs.