I got a good ideas for the new system
How about the dev put a limit on how much influence you can get?
An example would be title and renown, where if you are a duke, then you can gain lot more influence than a commoners or a baron would gain by delivering letter and errand and at some point, the commoners/baron influence stop growing until he either get a better title or gain a lot of renown
As I keep thinking of this, there's a lot of factors that have to be considered when putting a limit like relationship, council, marshal, character (like role playing a honest mercenary, trader, bandits, etc).