Jim243, I've tried your suggestion with chamber bore sighters as well as anything else that'll optically align bore axis with scope axis so they're parallel at any range, then adjujst the sight vertically down range to the amount of bullet drop plus sight height above the bore axis point. Cartridges used were .222 Rem, .243 Win, .264 Win Mag, .270 Win, 7x57 Mauser, .308 Win, .30-06, .300 Win Mag and .30-.338 Win Mag.
No more than a 1/4 MOA error at 200 yards, you say? None of mine were closer than 1 MOA at both 100 and 200 yards. The heavy kickers had a greater error; the 30 caliber magnums were a bit over 2 MOA.
Your method assumes the rifle will not move from its aiming axis until after the bullet's left the barrel. That never happens; not even with a 13-pound 22 rimfire match rifle.
Best proof of this I know of is shooting a team match with all members shooting the same 30 caliber rifle and ammo. There's easily a 1 to 2 MOA difference in sight settings for a given range zero. That's because we all hold a rifle at different angles to our bodies and present different amounts of mass behind it.
Or, with a rifle that's very accurate and sighted in perfectly for you, put that collimator in it then see where the barrel axis points relative to were your sight's pointed.
Note that a zero one gets shooting their rifle resting atop something on a bench will be different than shooting an unsupported field position; prone, sitting, keeling or standing.