My proposal to end the siege wars:
1 - Increase the siege population cost from 3 to 5.
2 - Increase the maximum population from 200 to 220.
This 2 changes would achieve:
- In situations of max pop reached (very common in the imperial siege wars) the cost of having siege instead of units increases.
- To avoid seeing a general reduction of the fielded units due to the siege pop increase, the max pop of 220 allows to field exactly the same number of units as before, assuming 10 siege engines are build. (Before they took 30 pop, with this change they would take 50 pop)