The similarity of isotopes for earth and moon would not seem consistent with just a glancing collision, with survival of a large intact portion (lacking core) of the moon.
In contrast, might tidal effects of earth result in a twisting (stirring?) of a band (i.e. tube) of matter in some sort of asymmetrical orbit after collision of pro-earth and a planetesimal; a dynamic 3-dimensional mobius strip effect? Might such twisting and turning i.e. kneeling, be more plausible than any direct gravitating of orbital matter? Hence shortening the duration of moon formation? Might a similar process shorten duration of terrestrial planetary formation?
Also perhaps another effect: a larger surface obstructing ‘fluid’ flow; thus resulting in an accumulative enlarging object? Then would latter onset of spherical shape for object seem consistent with a gravitational contribution?