Have they improved under Simons? They've found Yadav and maybe Aaron, but I think those guys would have been unearthed no matter who the bowling coach was. What about Ishant? Or Sreesanth? Or Irfan Pathan? Have the established bowlers improved at all under Simons?
Varun Aaron, no. He's been to the MRF Pace Academy, National Cricket Academy and the AIS Centre of Excellence. He's your regulation pipeline rookie, in the system since his teens. It's almost wrong to suggest he could have been unearthed. They planted him in the earth to begin with!
Umesh Yadav, more likely. Not a serious junior, he got on the radar in the 2010 IPL after a couple of good Ranji seasons and played for India soon after. He wasn't bowling 90 mph and wasn't even that useful a limited-overs bowler, but he was a clear find: a strong-looking 22 year old with as much pace as most of India's mature stocks.
Ishant Sharma is the interesting case. He seemed to have all the tricks in 2008, but between then and now hasn't made progress. Some suggested he was better back then, but he took few wickets, bowled few miserly spells and didn't have to do a whole series. He won a lot of hype for a couple of spells featuring pace, bounce and inswing; but not for length or efficiency. In terms of coaching, the big question is not whether he has developed since 2008, but since 2010.