One thing that bugged me about EU3 was that its combat was often unrealistic. The main goal of any war is always to wipe the enemy's armed forces. In reality, how often was an army totally destroyed? In EU4, I don't think armies should be destroyed (unless maybe around 0.1% persists). One reason why wipes are so effective is that it actually costs quite a bit to rebuild those regiments, while even if only a 1k remains of an army with 40 regiments, they will rebuild for free over time. My suggestion would be to add a separate slider, something like "reinforcements", which would determine how quickly your regiments would regain people. Also, in general, reinforce speed should be slower. That would mean that a battle where you actually lose 50% of your army will hurt much more than it does in EU3 at the moment.
Another thing that could be changed is that small armies simply cannot siege. Often, small armies are a nuisance because they block provinces; in EU4, it could be done that if there are for instance only 1k soldiers in a province (or less, I don't know), then they just stand there, but no siege is initiated. The province could still function normally, recruit regiments, etc.
A great thing would also be the concept of keeping troops in a town. If there is a 1k siege force outside, I should be able to raise 3k in a city, and then launch an attack on the sieging troops. The way it is now, it is very difficult to break a siege, as new troops have very low morale. Maybe each city should be given its own, local, manpower pool for such occasion. Furthermore, garrisons could just simply be troops that are stationed in a city/town - you could take them out, put more in, etc. If you leave a town empty, its revolt risk would rise sharply, etc. Fortifications would still matter, as they could increase supply limit, defenses, etc.
I think these changes would be a good way to eliminate the classic EU3 strategy of "wipe, occupy everything with 1k regiments". It wouldn't be necessary to chase armies around anymore, and sieging with small armies could actually endanger your own success.
Another thing that could be changed is that small armies simply cannot siege. Often, small armies are a nuisance because they block provinces; in EU4, it could be done that if there are for instance only 1k soldiers in a province (or less, I don't know), then they just stand there, but no siege is initiated. The province could still function normally, recruit regiments, etc.
A great thing would also be the concept of keeping troops in a town. If there is a 1k siege force outside, I should be able to raise 3k in a city, and then launch an attack on the sieging troops. The way it is now, it is very difficult to break a siege, as new troops have very low morale. Maybe each city should be given its own, local, manpower pool for such occasion. Furthermore, garrisons could just simply be troops that are stationed in a city/town - you could take them out, put more in, etc. If you leave a town empty, its revolt risk would rise sharply, etc. Fortifications would still matter, as they could increase supply limit, defenses, etc.
I think these changes would be a good way to eliminate the classic EU3 strategy of "wipe, occupy everything with 1k regiments". It wouldn't be necessary to chase armies around anymore, and sieging with small armies could actually endanger your own success.