Coaches help but yeah I'm not sure what percentage of the pie it is but more then 51% is on the player to work on their physical abilities. Be it strength, leaping, shooting etc. How many coaches did Shaq have in his career and he always sucked at free throws. That's on him. Coaches don't get the credit for how good Korver is at making 3s either.
Just a little reminder of what coaches responsibilities are
1) selecting the player to recruit
2) getting the recruit to sign LOI
3) formulating strategy for individual games
4) deciding on the starting line-up
5) deciding how many minutes each contributor will get
6) implementing strategy during game
7) adjusting strategy accordingly based on conditions of the contest
8) deciding which position each player will contribute at
9) deciding what tasks players will focus on during practice
10) creating a development routine to improve the raw physical ability of the players
11) hiring assistants that have the ability to instill discipline among the players as well as improve their technique thru instruction and repetition
12) inspire his charges to perform at their maximum ability
13) figuring out how to assemble the pieces so that they over-achieve as opposed to under-achieve
14) earning their paycheck
15) using their position to further their child's professional ambitions (strike that, I forgot which board I was posting on)