Well, I´m not here to develop a game, I would like to do so, but I don´t have time, but from my point of view boosting the effectiveness of tactics is not a big change at all.
I guess you want some example like you and other player had said. Well, let´s put some example which came to my mind in a few seconds whithout considerations about the implications. Just a remainder, the point is to show an example o big change, not to show a big change which will improve game experience. The second thing will require to reconsider a lot of times and I don´t have time to do so
Some examples:
change the structure of leagues. Now is more or less, 1-4-16-64-256 an so on... lets put it like 1-4-8-16-32-64-128 and change how much we earn for tv in each division and a lot of more things you will need to change in order readjust everything
Another big change, lets put some more juice in the game. create a few more skills for players and then you probably should change something in time trainings, but I can assure I could come up with at least 10 more skills in five minutes
I assume you don´t like this changes at all, but I will propose a couple more in order to show you what a I consider a big change
lets change how it works salaries in the game, for example lets put a maxim for each división and a penalizations for which teams that surpase the limit, and the fine should go for the rest of the teams on his own division. Something based on NBA system but with some changings
lets put another change, instead of organize teams for countries, let try to create another way to put into groups, in a way we have for example 20 regions withs symilar numbers of divisions and teams, and then reorganize internationals competitions
Just a remainder, I´m not saying that I would like to see these changings, just I want to show you -like you ask- what I consider a big change