If your theory is correct then why don't past results support a more variable mix of success? In almost 11 seasons the best team usually wins. Since season 3 there's been 14 cup and league trophies split amongst 3 teams. The balance of power from top to bottom has been extremely static.
Just because the top teams continue to have an entrenched advantage, doesn't mean his theory is incorrect; if you removed enthusiasm you might well have more than 14 cup/league trophies split between 3 teams. I think there are a couple reasons why the balance of power has remained relatively static:
1) At the top divisions, everybody is a pretty good manager, so you're not going to rise through the ranks very quickly on human skill alone. Even if you are the very best manager, you are still only marginally better than the other very good managers around you, and it is easy to imagine it taking seasons of being a marginally better manager before your team can catch and then surpass the old guard.
2) As you said towards the end of your post, the friendships that develop between managers who've been at the top level together for 5+ seasons tends to lead to an unofficial league-wide mTIE anyway. If you believe mTIE is an advantage to the top teams (and having followed this thread, I do), having these understandings between friends (who are probably coincidently also the top teams, or they would not be staying in the top division for 5+ seasons straight) only adds to the pile of advantages entrenched teams already enjoy.
The way I see the issue is that asking whether mTIE is an advantage/disadvantage for weak teams misses the point; weak teams are not really competing with the top teams, they are competing with each other to avoid relegation. The teams a league-wide mTIE really hurts are the decent teams who have moved beyond fear of relegation and are now trying to challenge the top teams. These are the teams
just below the top, who are trying to dethrone you, the ones who DO have a legitimate shot at stealing a game by going normal on the road, or being able to protect home court even with a TIE. Taking enthusiasm decisions away from these teams means giving them one less weapon to try to use against the older, stronger teams, and it extends the number of seasons a decent team needs to grind out marginally better improvements before he can compete with the big boys.
mTIE is sort of like a ceiling that says, 'We'll make it easier/simpler for you new teams to go from bad --> good, but we're going to make it really, really hard for you to go from good--> title contender." That is an outcome that is ultimately in favor of the already top teams, any way you slice it.
I personally believe a league-wide mTIE rule would make things more boring and hurt more teams in this league than it would help in the long run, but you guys earned your way here so you have the right to play however you choose. What concerns me more is the idea of using a league-wide mTIE as some sort of statement/boycott to pressure the BBs to change the whole enthusiasm system.
As everybody probably remembers from their younger days, enthusiasm offers a ton of options for teams in lower divisions looking to make a playoff run and steal promotion, continue a cup run by surprising a stronger opponent, etc that aren't as applicable to teams entrenched in division one. I worry about seeing the system scrapped just because it's positive aspects are less obvious this high up the food chain.