Q... any time you need a building to function in such a manner, ya gotta use a footing. Here, it's not a requirement (gray area, really) and many additions to houses use Sono-Tube footings (as you described, more or less). I have been called in many times to assess damage to such structures from differential settlement (what happened to your structure). In all cases, it was the young engineer or tech that signed the design drawings that paid the price... for taking a small fee from a shifty contractor. Simple pier footings are just "risky", ESPECIALLY in frost country as the opposite of settlement can happen.