apples to oranges
Comparing an M1A and a Ruger Scout ( or one made by anybody else) is not a
same-same comparison. But,.....you mention "long range", so we can start there.
A scout will typically have a low powered IER scope. Dedicated "scoutscopes" are typically 2.5-2.75X, ala Leupold and Burris. Such an optic is not ideal for long range, as it makes target ID and precision difficult. Note what dedicated varminters and match shooters bolt on their rifles. Big bell, big tube, high x count, typically high dollar scopes. An M1A will take such a device easily, not so a scout (without defeating its role as a GP, portable firearm w/ backup iron sights)
A Scout will have a short barrel, 16-20 inches. A full size M1A will have a 22" tube. The M1A will have a longer sight radius with irons as sights, and a SLIGHT edge in velocity with any given bullet weight, yielding a tad better trajectory. Not much , but perhaps enough to forgive an error in range estimation and sight alignment way out there. Again edge to the M1A.
M1A's are commonly used as match and competition rifles. I doubt anybody will take their Scout w/ its 2.75x scope to an XTC 3-5-600 match or to an F/TR 1000 yd match. Well I guess they could, but it would be a novelty.
And I doubt anybody will run to get a Scout as a designated marksman rifle, though it could serve as such. ( the Germans in WWII used a LER scope on the Mauser 98, but it was not popular if I read right)
Finally, I suppose sheer mechanical accuracy, groups at 100 yds from the bench, given equal sighting systems, ammo, and triggers, etc, the bolt rifle MAY shoot smaller groups. But taken as a system, using larger optics,match barrel, good trigger, etc, past 100 yds, I think certainly past 300, the M1A would come out on top.
But......an M1A w/ a big scope, maybe a match barrel, bipod, ....is not a particularly portable device at least when not compared to a scout. The utility of a scout, enough rifle for medium range (say 300 yds) on medium game and as a GP rifle is what makes continues to keep the scout rifle alive.