Well, if ordinary soldiers who shot at best 10 times a year, somehow hit the target at 328 yards, then a very experienced shooter would have been able to get even more.
The figures that give around 20% at 300 yards are based on volley fire on a target representing a whole enemy line
. It's not like you would get 20% chance to hit a single man at 300 yards. Moreover since you wanted to stress the difference between actual battle accuracy and "technical" accuracy, you wouldn't pick a large target to check actual accuracy... Indeed, in a battle, as you admitted yourself, you will most probably not see as well after your first shot, and therefore your accuracy will decrease, so firing at 300 yards is clearly not realistic, not even at 200 yards.
Regarding your comparison with bows, range is certainly not the main reason for which muskets were used, especially if we look at the actual accuracy in battle, which was more than very low as I already said. The reason is that muskets are much easier to use than bows, you don't have to be very well trained to use a musket. If you look at your own figures in one experiment "well trained" soldiers would put 53% of bullets on the regiment-sized target at 100 yards while ordinary soldiers would put 40. So one has to wonder whether it's worth the time and money to train soldiers and the answer is clearly no, except for a few elite troops.
Longbows had good range and could fire much quicker. I'm pretty sure that longbows would have been deadly against an infantry regiment. The problem was that using bows required much more training, and also they didn't had the same kind of melee defense, especially against cavalry.
Arrows were used efficiently by Cossacks during the Napoleonic Wars:https://www.rbth.com/arts/2014/07/29/how_russias_steppe_warriors_took_on_napoleons_armies_37029