If you are going to worry about the differences as they stand today I think it is wiser to argue the position of new teams yet to join BB (as to grow the game needs to be attractive to them) NOT so much the teams that are already long term addicts.
Merging everyone would solve the problem for only a few, and cause hardship for most of the rest. You are talking about a much bigger pyramid here, and though I have a good chance to promote to USA III this year, your solution sends me careening to the bottom of the pyramid, while players who have been able to take advantage of the easier growth in a smaller country now propel past 1000's of users from places like Spain, Italy, Poland, USA, etc.
Changes need to be made often in these types of games where there is an imbalance or eventually the imbalance will keep the game from growing. If we saw that over time the imbalance between being a new user in Spain vs a new user in Scotland slowly leveled out, there would be no need for change, time would fix the problem. In this case, I think the gap caused by the imbalance is widening with time.
Any solution will anger some people, but that doesnt mean we should avoid a solution and keep the problem either. Perhaps if the bonus money for promoting to a higher division or winning your series were scaled from the bottom up instead of the top down it would be more fair and balanced. You should get more money for going from a Div II to Div I in Italy than you should for doing the same in Japan......no offense, but I think we can agree that it is a tougher acheivement.