Can putting frozen food in a hot ceramic pan cause a thermal shock

I have a ceramic-coated pan too, and always treated it with care (plastic utensils, no overheating, etc.) It failed too, after some time (I think I've had it for 9 months now, and used frequently).

Unlike a failed Teflon pan, it does not look or feel any different. But while at the beginning it was superslick, with everything gliding right off it in a fluid motion, now it is only moderately non-stick. I can still use it as normal, including for such problematic cases as omelets. But if I fry without fat, I need a spatula to dislodge the omelet from the surface. In contrast, when I bought it it was like polished ice. It is still more non-stick than, say, enamelled or seasoned iron, and definitely better than stainless steel. But it isn't as good as a good-quality PTFE.

If the non-stickness keeps at this level, I still think that it makes sense to buy it, if you have the money. They are expensive, especially the brand-name ones, but can give you nice, even heating. While they will give you less non-stick performance, they are more robust than PTFE - metal utensils don't damage them, they don't overheat as easily - and I found the non-stickiness sufficient. The nice thing about them is that the quality ones aren't thin aluminium, mine has a 10 mm sandwiched steel bottom - you don't get this in PTFE. So they can be used for applications impossible with PTFE, and will give you a better heating in the cases where PTFE would have worked.

On the other hand, you can decide to go traditional, with a combination of PTFEs for the sticky applications and iron or steel for everything else. It will probably give you a better tool for the stickies, as long as the PTFE coating itself doesn't fail through accidental overheating. It is up to you which style you prefer, but the ceramics aren't the panacea they are touted as.

The theories that have come out in comments are most likely right on. Cast iron is special in how well it retains heat. Give cast iron ample preheating time, and you can drop in cold food without a significant drop in the temperature of the pan. That equals crispy. Even a pretty good and heavy non-stick pan is not going to give sweet potatoes the kind of crisp you can achieve with cast iron.

You mention higher sides in the non-stick pan. That alone probably wouldn't make much of a difference, but considering that you're already seeing a greater drop in temperature as you put in the potatoes, the higher sides would hold in more moisture in the cooler pan. That is not a friend of crispiness.

You say that you preheated both pans to about the same temperature. I actually hope your memory is a little off on that :) One of the great joys of cooking with cast iron is that you can and usually should pre-heat it to a quite high temperature without damaging the pan. Teflon, on the other hand, should never be preheated beyond a very moderate temperature for a very short time. Some people go so far as to say that you shouldn't preheat it all. So if your beginning temperatures were about the same in the pans, they shouldn't have been. After you put in the potatoes, forget about it. You'll never get the same kind of crispy sear with a teflon pan as you will with cast iron, even if you don't know how to best exploit the advantages of cast iron.