The objectives of the Army marksmanship system, he explained, were to quickly and cheaply train large numbers of basic, effective combat marksmen...
This is true with the emphasis on 'cheap' unfortunately. Reminds me of the old saw "You can have it cheap, quick or good -- you can have any two but cannot have all three."
...with units developing precision riflemen for combat and competition.
Peacetime thinking. Willard Wyman was a reasonably smart if mediocre General (all Generals are sort of mediocre; the really sharp guys get killed off by their contemporaries on the way up as unfairly over competitive). In 40 years of service, he had a little over two years of 'combat' experience (all high level, thus the quotes).

Importantly, if the units do it, the good units will do a decent job, the poor ones will not. if it's worth training, it's worth training properly and thoroughly. Tabbing difficult and expensive training tasks out to units is a cop out
... Unfortunately Unit and Soldier mobility and dispersion dictated there would always be a need to cover gaps and terrain using designated squad riflemen (distinct from snipers) who could effectively shoot and kill targets at extended distances to 500 meters.(emphasis added /kw)
That says it all -- Wyman took the wrong approach. He had and has a lot of company...