I wonder if it was the other team's defense was forcing you into bad shots or shots out of his range.
BB-Forrest has described the game engine as different players taking looks at the basket, and shooting or not based on the defense, offense, shot clock, etc. It could have hurt to lose Garza so early since that just meant more of load for Cosby.
70% of shots from the SF and SG seems kind of high. Were the shots coming at the end of possessions?
I don't think the game engine "knows" the skills of the players. Otherwise you might have the splenderific passer passing to the splenderific shooter on every play.
You might want to build up his range to match his shooting. Since JS is a skill for PF and SF, it must include 10 footers and 12 footers as well, and just a player is a guard, he might not automatically shoot better from 20 or 25.