There are some imbalance between top teams in B3 competitions but that only affects a few teams. Your point about salaries balancing out overtime is true, if the big fish-small pond teams buy top salary players.
Nonetheless, the affect on teams in one country competing with teams in other countries ignores the fact that everyone in your country is in the same situation. So from a domestic point of view this issue is irrelevant.
What does matter is how much teams in the other divisions in your country are making. If the profit margins are large between 1 and 2, 2 and 3, etc..that will have a big effect on movement up and down. It seems like they are large enough to prohibit much turnover between levels, but I don't have enough info to say for sure.
"Well, no ones gonna top that." - http://tinyurl.com/noigttt