Your assumption that the long training was purely because of the massive draw weight - and the massive draw weight was purely there to defeat armour - is flawed.
A bow is a physically difficult thing to use. The movements, stance, breath control, drawing to precisely the right release point, learning a quick, clean release movement, judging distances by eye, judging the indirect arc of the arrow's flight, judging the wind, and most of all: everything, every single little thing - has to be done exactly the same for the next shot, otherwise that arrow will fly differently.
The training also involves maintainance of the bow - of the bowstring - of the arrows.
You have to get all that right, even for a bow with the smallest draw weight. And you have to get it right every shot.
Plus: Draw weight doesn't just affect penetrative power. Draw weight is what gives you range.
You could forgo muscle training, but you'd produce a generation of archers who were useless at fifty yards and who tired easily.
The 'no armour' argument is missing the point. Sure there was little armour in the 18th c. But only because bows, etc. were no longer a threat.
If the bow had been reintroduced on monday, the armour would have been back by friday.
One of the factors which favoured the musket was production. Muskets could be constructed in large numbers, production-line fashion, by semi-skilled labourers, whereas bows were hand-made in small numbers by craftsmen.
But the biggest factor was a social change in the men who made up the armies.
Wherever you find the bow as a battle-winning weapon, it is in the hands of a social group whose entire lives revolve around its practice. We won't mention the English longbowmen, but the Huns, the Mongols, the Hamians (who provided most of the bowmen in the Roman legions)... these were people whose way of life was dedicated to the practice of archery.
Archery does not make much contribution in battle UNLESS you have some of these dedicated, lifelong bowmen doing it.
But in the 17th century, we start to enter the age of mass conscript armies.
You can no longer pick and choose from a trained elite. You have to take what you can get, and as many as you can get.
This means sentencing criminals to serve in the army, taking people from areas of economic hardship, like Ireland, and taking people whose industries have collapsed, like the weavers who made up a large part of Wellington's army.
These people are essentially civilians, who need to be quickly trained to use a simple weapon, en masse, responding to simple commands.
The answer, at first, was the pike.
This was soon augmented by the matchlock musket. But the matchlock was a slow weapon, and required protection while it reloaded, so the pike remained on the battlefield along with the matchlock.
It was not until the advent of the flintlock that a simple, reliable weapon for mass conscript armies really arrived.
The idea of recruiting mass bowmen without years of training has been tried.
In the Hundred Years War, the French issued instructions called 'Ordnances' for the raising of armies. (These forces, therefore, were known as 'Armees d'Ordnance'.)
Being particularly short of archers, they gave generous tax breaks for volunteer bowmen, and raised large numbers.
They proved utterly useless on the battlefield. Even large numbers of them accomplished nothing.
And the bow WAS present in the Horse-&-Musket era.
During Napoleon's ill-fated invasion of Russia, Kalmuk & Baschkir tribesmen used bows against French piquets and patrols.
The Russian tribesmen were competent raiders and bow-hunters, but they were not dedicated, full-time archers. Their bow use, even against the unarmoured French, was considered nothing more than a nuisance. The French called them 'Cupids'.
History has shown again and again that unless archers are real experts, then even large numbers of them make little difference on the battlefield.
Hope that helps!