By my count a fully upgraded city would have 180 siege health - that's 18 turns before battle if you don't spend any money!
That sounds terrible but it's very easy to fix - just change a few numbers. Hopefully if 10+ turn sieges are the case, the devs will realize that nobody wants to park their army in one place for that long and change it in a patch.
So far I have mixed feelings on the sieges. On one hand, I don't like that random armies can no longer capture towns - this eliminates some of the tension.
On the other hand, I like that you are now able to destroy city walls before the fight even begins. I'm playing through AoW:SM now and base defense battles are hilariously easy to win. AI is too retarded to attack your towns properly and you can beat an army several times your size if you have a handful of ranged units on the walls. But for the player it's not a problem because you can do shit like: initiate the battle with a few heroes, bombard the enemy rangers with spells from your mage ruler and heroes, retreat, then attack with the rest of the army and win with minimal losses.
Being able to eliminate walls before the battle will hopefully make the AI a bigger threat to your cities.
If the games had AI that's not retarded this wouldn't be necessary but alas, this is the world we live in.