And the community average will include low skill labor in high numbers which distorts the average.

The letter writers comparison of similar job skills in other parts of the country was effective.  He's also smart to include total compensation, not just salary.  (vacation time, personal time, education, club memberships, professional training, etc.. can be a part of total compensation)

I believe in collective bargaining, but it's always going to be tricky.   There are many ways to hide profit.  And, other interested parties, (owners, shareholders-share price or dividends), executives class management,  are standing in  the front of the line for profit distribution, before the wage earners are considered..   It's got to be tough for negotiators to discover this information.