There is a degree of truth in that an engine with a stop-start function will experience slightly more wear than one that does not, even though engines with this system built in are designed to ensure this is kept to a minimum. As you say, a few seconds of the engine being off will not result in all the oil returning to the sump, and it is far less wearing on an engine than starting from cold where the oil is also cold and is not yet circulating. If you are concerned about engine wear, regular oil changes will ensure your engine has the best possible protection, and most vehicles have the option to turn the stop-start function off.