Assuming (I know, I know) that a lightweight rifle is intended to be a carried, hunting rifle then the accuracy potential of either barrel when measured by shooting groups is very nearly a moot point.
My prime concern with such a rifle is whether the first shot from a cold, fouled bore goes to POA each and every time. It's nice if the second and subsequent shots also go to POA but in the hunting game that first shot is paramount.
If first shot accuracy can be obtained with either length then the ballistic advantage provided by the extra tube length is welcome.
I also think that the slightly more forward balance point afforded by a 24" tube is advantageous for steadying up on target when shooting offhand.

I don't consider a #2 contour to be a pencil barrel either. Especially if the bore size is such that you maintain at least .150" wall thickness at the muzzle.

For me, 22" is as short as I'll go and 24" is perfect.