Doing more than 3 dives in a day is against agency standards.
I'm required to spend, at a minimum, 12 hours in the pool and in the classroom. 16 in each is preferred. We do include a number of skills that other agencies do not as part of the required course.
I have found that after about 2 hours in the water people start to get tired, cold, and lose focus. Not what you want in training to be active in a hostile environment.
Muscle memory is also a big part of training and diving safely. In OW, your responses need to be as smooth as possible with little thought. A reaction to a flooded mask should be instinctual.
If your buddy gives you an out of air sign, your hand should not hesitate to donate the octo or the primary. You likely can't do this if you've only done the drill once.
In some cases, I have had to completely redo an OW course for a diver trained in one of these rushed, hope to survive, classes. Especially when they go from a warm water, unlimited vis experience to our low vis, colder water environment. They are not in any way prepared.
Standardized training can work IF it is supplemented with information, practice, and skills suited to each individual environment. That takes time.
Even in a warm water setting, there are things that should be done to ensure the divers are able to dive unsupervised when they are handed their OW card. They should not need any assistance from a dive pro. Tough to get them to that level in one or two days. Even though RSTC Guidelines require that level of competence.