I agree that lenses and the films and photos produced through them should be as free from distractions as possible (except when the regisseur wishes to display his optics and that actually contributes to the result rather than being just irritating).
BUt back to the issue of the real worth of the 50-300ED. My copy has stood the years well (and has the original sunshade). BUT it is so heay and cumbersome to drag around (compared with carrying the extremes of its focal lenghts separately, plus the small and sharp midrange 105, that I rarely use it. Two zooms could cover a larger range, be smaller, in sum weigh less while giving better results.
p.