Suns' strategy is trading basket with you. They are faster and shooting better than everyone. There is NO WAY, you can ask Rockets and Yao just to stay in and cross their fingers. They will make most of the shots if uncontested. Besides, there is no rebounds in the paint for Yao, if it turns into a premieter game. Long shots cause long rebounds.
Yes, the Rockets have to slow them down, by better defensive rotation, better communication in switches and defending PnR, NOT by daring them to shot. They will make those shots you give them. Yao has to come out to keep the opponent center honest. He's 7'6! It's tough to run back and forth, but he has to. It's NBA, not a pickup game. Suns are a very good team, it takes smarts and EFFORTS to beat them.
I always see lots of fans talking about zone defense. It's not easy to run it well. There is one major shortcoming of zone defense: it's poor against good 3 pointer shooting teams. You can only go out, rotate quickly, make it not so easy for them outside, so you can beat them inside. If you just duck in, let them have the premieter, they will beat you 10 out of 10 times.