Siege Mechanics, change?

Normally one would have a plan to clear troops from the city prior to sending sieges.  This might include having adequate troops in the siege army itself or sending troops to clear the city separately.  Since pretty much anything moves faster than siege armies, the argument about having armies days away doesn't make sense.  And given how serious a siege is, it doesn't seem onerous to expect that level of planning.

I see no problem.

If you're serious about taking/razing a city, send additional forces from home to clear it before the final assault.  This also means if you're serious about defending a city and have the forces to defend, you actually can at least save the husk, along with its research, position, and commanders.  As it stands, the onus is properly on the aggressor to coordinate sufficient troops to greater effect than the defender, else return home empty-handed.