Of course they do and under normal circumstances it's not a problem but when you bring in the specific dynamics surrounding unions it becomes another matter. I worked in management for a company where at the time we were trying to get the employees to dissolve the union, there were never conversations where we lobbied the members and union representatives weren't present. I think it's inappropriate for those types to conversations to take place when I assume the union wasn't given the opportunity to have someone present.
To your other point, I hear you but also the description of market size is nebulous to me anyway. Let's take the NBA for example, since 2000 the only titles not won by top 20 metros are San Antonio (likely to be top 20 by 2030 and the 7th largest city in the country currently), Cleveland, Milwaukee, and OKC. If we shift San Antonio to the other bucket it's 21 from 24 (excluding Toronto) in the top 20. It's also 17 that are top 14 metros or bigger.
NFL is a little more slanted because of KC but it's still 15 of 25 are top 20 metros and its 17 of 25 if you extend to top 22 with Baltimore. I just don't believe that a salary cap would make baseball any less slanted, the teams are primarily in bigger markets, the top 3 cities have 20% of the teams and the top 10 metros have 43% and the top 20 have 66%.