If you want to argue RW is underpaid, go ahead, but his salary has almost no influence on FH market value. First, the whole small sample issue, and second, market value is not about rewarding past accomplishments.
Yes it does. It's not the biggest factor, but it's there (and not just RW, others). Almost all decent professional jobs in this country have a salary that has a lot of factors that goes into it - one of them being what other people in a similar situation as yours makes at a variety of different companies. How the company chooses to interpret that differs. Some offer right on the average while others offer above the average.
Your past accomplishments and expertise definitely play a role into it, especially ones in the last handful of years. If you don't think this, then you don't have enough experience in the professional world in how salaries are actually figured out. I speak from experience on this. Thinking that prior success, even for coaching sports, has no influence on salary is extremely ignorant and naive IMO. Obviously there's outliers, but on average it follows this trend for many types of jobs.
The sample size may be low, but you better bet your *** that someone especially who is trying to save just a little bit of money is thinking "Well ____ and ____ have been to the Elite Eight five times each and you haven't once, so we're going to offer you less." It's common in the professional world and I have first hand experience with helping deciding these things just to save maybe $15K/year.
It's not the only factor that goes into figuring out salaries - there's many - but it is one factor of the handful. I speak from experience and I have no doubts that it's one of the factors for coaching too. The trend setters are the ones who win championships and the schools will just offer them much more. Hopefully someday we can say Hoiberg is a trend setter and it would be awesome if that was at the end of this season. I think he will get a raise this year, but not to the $3 million mark yet.