Agreed. And, if the circuit breaker is not within 50' or within sight you'll need a local disconnect means.
I think your first assumption is the more correct one. Why would a person wire both heating elements so that they come on at the same time ? To shorten the recovery time AND void the manufacturer's listing ? I don't think anyone of us would risk that. Had to be a HO job IMHO.
I remember doing exactly that many years ago - except we ran an individual branch circuit for each element and rewired the WH so upper and lower elements were independent of one another. This was in a cheese manufacturing plant, the water heater supplied a machine that washed the "rags" used in part of the process, and they were washed and reused every "batch". Problem was the WH did not recover fast enough between batches until we rewired it this way. Voiding listing or warranty was not a concern to the owner, domestic water heaters cost nothing compared to most other equipment that was in use in this process. though I still could never figure out why they didn't use the readily available steam in that plant to heat the water for this particular part of the operation.
That actually isn't always that bad of a thing, when toilet sees a lot of use on hot humid days, the tank and/or water pipe won't "sweat". New toilets are only supposed to use one gallon per flush as well.
How about replacing a 100 HP motor that is about 50 feet from grade level, but inside an enclosed industrial structure so you can't just pull a crane up nearby to do the lifting?
One of my neighbors did some DIY plumbing and put the shower valve in backwards. He had to cut into the wall to reverse the pipe connections.
