I really dislike all of the shower versus bath calculations, because they compare a full tub versus a five minute shower. Even a ten minute shower is less than most people take, and left us be honest that the average american woman would use much more time than ten minutes to shower, shampoo, and shave.
But, let us use the ten minute low flow shower (same as 5 minutes shower with regular nozzle) versus a full bath. It is already my contention that this is an inefficient bath technique being compared against a very efficient shower technique, but this other website estimates that about 19 minute shower is about equal to a full bath tub. This is lowered to ten minutes with a normal shower head that is not low flow.
https://www.sciencefocus.com/science/how-long-does-a-shower-have-to-be-to-use-the-same-amount-of-water-as-a-bath
I think a twenty minute shower is about normal for a deep clean. We arent talking about a quick suds and rinse, but one that would compare to a lengthy bath. To me, the average bath matches the average shower, but a bath with minimizing techniques easily is more efficient than a mininizing technique for a shower. A shower is wasteful, and I think there is a campaign to make you think that a shower is the most efficient.
Want to be efficient? Take a shower with the bath drain plugged and use the water. This is also a valid way to determine how mi h water you use during your shower, just remember that a truthful measurement would come from a deep clean, not a shower rinse.