I think the point of the merc change is to do multiple things:
A. Stop 1700's+ eternal wars where both sides have full mercenaries and are just blowing off their 10,000 gold they have laying around. Both sides sit at 100+ mercenaries losing 50 gold a month but it'll take 20 years just to get through the gold before anyone even has to take a loan.
B. Require people to merc up early rather than mercing up in response to losing manpower. you can't just replace your army with mercenaries if things go wrong.
The problem as I see it though is that by ultra late game when you're sitting at a 300 force limit and quantity (which is being changed to increase merc limit for some ungodly reason) you're going to have a 120+ merc limit. That's plenty to wage eternal war with, and with quantity increasing the merc limit it's probably going to be closer to 170+ I imagine. It might stop a guy from just mercing up his entire force limit and fighting to the end, but it won't stop two players from fighting eachother until the game's end, just constantly throwing their armies against eachother.
It's clearly better than what we have now, I suppose.