Gentlemen
It is absolutely true that for a given bullet at useable speeds, the faster you start it the faster it loses velocity. If we choose a .308 165g Nosler AccuBond as an example and launch it at 2800fps and 3200fps, this is easily seen. Lets further assume, for trajectory purposes, that both loads are zeroed for Maximum Point Blank Range for a 6 diameter target (3 maximum rise):
Range Delta Delta Delta
FPS FPE Trajectory
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000yds = 400 879 0.00
100yds = 382 787 -0.26
200yds = 367 711 +0.69
300yds = 352 705 +3.06
400yds = 338 631 +7.28
500yds = 326 503 +13.22
1000yds = 232 241 +92.85
The numbers above are from the perspective of the faster 3200fps bullet, relative to the slower bullet. It is clear the faster bullet slows down faster initially, but if you compare them at equal velocities, they slow down at equal rates. This, of course, occurs at much different ranges in this case the faster bullet has a 220 yard advantage, at which range it matches the 2800fps of the slower bullet.
As has been pointed out, they only become equal when they hit the dirt, and the slower bullet will do that much sooner.