No I wold say not. it is important. In a good bench load every aspect is important. Every round must be consistant with every other round. the velocity out the barrel is where you need the consistancy. If there is an inconsistancy in any component the velocity will not be consistant. Powder and bullet factors I would think are the greatest elements of error. However I think you will find the factor that separates the top 1% of the shooters is the ability to dope the wind. in other words, the shootest.
is neck tension the most critical aspect of a good benchrest load,I would think that it is. what are your thoughts??