this is a bit misleading. you go from talking about his last 2 years for games played, but then you dont specifcy that the 36% shootings was just this past season as opposed to that same 2 year sample. he had shot 38% from 3 the year prior, which vassell only bested once in his career (38 game sample size for devin that year).
in murphy's 4 seasons, he has shot 38.2%, 40.6%, 38.0%, and 36.1%, with a career average of 38.3%. vassell's career average is 36.9% on slightly lower volume.
murphy is a better shooter. he also is a much more comfortable off ball player in general. much quicker decision maker. more athletic finisher and explosive driver. his defense did take a step back last year, but defense hasnt been a calling card for devin for about 3 years now. but still, if you compare their recent histories defensively, murphy has been better. and if we are talking about a team likely starting Fox/Castle in the backcourt, Murphy has more length and is better equipped to defend 3's
vassell has more on-ball juice than murphy, but i dont know how much on-ball vassell is contributing to winning at all anyway. his on-ball game certainly doesnt have much value for the spurs now, and if anything comes at the expense of their team success.
its not really a question that murphy is both a better player than vassell and a better fit for the spurs, but is he worth vassell plus multiple firsts... no, i dont think so. the spurs dont feel "one piece away" and the next time they deal multiple picks for a player, that ought to be the scenario