Who is he? What has he done?, I dont see Improvement.
Edit: He is the NRG coach.
He is more of a developmental coach, not a strategist. He will help players improve on game sense/decision-making. For example, TenZ asked him to help because he wasn't making the right decisions sometimes in pro games. Now we see that he doesn't make those same bad decisions as much. (Not saying that it was just JoshRT's work, but it probably played a part.
you can trust Josh, he has brought up many teams from the T2 scene into a higher level, even competing in some of them himself. With players from his rosters early on in the scene now being signed to T1 orgs. What Firell said is also true, players will develop over time, for instance with s0m on the IGL role.