Hardly. In fact its a very viable and useful tactic. Just because you can do something doesn't nescessarily mean you should. In fact, I did it more than once as the Maks and by the time that was necessary I was already a big deal, so its not like I could not have. Its just that I didn't want to suffer from battle fatigue and I wanted a slower pace to my overall expansion, so I could consolidate and remove some of those lovely culture penalties. As long as you give the cities to an erstwhile ally you can have a lot of peace. In fact, since the AS in my Mak campaign was still friendly, if not allied, to Pahlava I just took some eatern provinces after I had expanded as far east as I wanted and gave it to them. Voila! Now I've had a peaceful eastern border for over 25 years.