I'm overthinking the subject of a thread? I think coaching is considered to be an indepth subject. A fair amount has been written on it, even in terms of cycling. The ways in which it has changed in recent decades seems of interest. If not, overlook.

First, new racers don't know about form or how to get it. A team of uncoached/semi-uneducated racers could use a coach perhaps. In the old days anyway. (But the old days were also a time of huge ignorance and little communication, with only a few simple books, and even then when info was king and hard to get only a few local-type/regional/newbie/developmental teams bothered with coaches). (I guess we were really rare/lucky in Detroit to have a coach who worked with every level -- from kids, newbies, regional-stars to world champs.)

Second, how impt to success is the DS? Seems likely from what you describe about the DS -- even though, you're right, his role is limited -- that it could still easily mean all the difference to success.

Of course quality is also determine. But efforts along these lines might pay off lots bigger than going it alone -- certainly for most, though obviously there would be exceptions.