The Hypnosis Question | Bulbagarden

Let's use Malamar as an example since it is stated in the Pokedex as having mind-control abilities that are stronger than other Pokemon. Now, let's go to its debut episode and review what events occurred and what we can deduce from what we saw. A singular Malamar can control multiple individuals, as seen with how it controlled about 8 individuals in that episode. It can also control them for extended periods of time as shown with the Officer Jenny in that episode.

However, the Hypnosis has limits. Ash and Meowth were able to to defend against it by having Meowth scratch up both of their faces while the Hypnosis was being applied, which somehow disrupts the process and causes the move to fail. Hypnosis also seems to require time to fully take hold, as Meowth was able to react to the move and apply the scratching as previously stated. Ash and co also get out of this dire situation when Clemont's machine from earlier crashes into Malamar, which causes it to lose control of its victims. It would seem that the user of Hypnosis needs to retain some level of focus to maintain control over targets or at least precision control instead of just putting a target to sleep.

Drowzee and Hypno are also prominent users of Hypnosis. From what I remember from their debut episode the whole incident of disappearing children was an accident caused by lingering psychic energy from Drowzee and Hypno being used by a bunch of rich people to treat stress and insomnia. Misty subjects herself to Hypnosis later in the episode and we see that a more deliberate application requires both time and close distance to accomplish the same effect on someone (relatively) older, the other affected children looked very young.

Drowzee was also featured in one of Team Rocket's (not Jesse+James) schemes during the Orange Islands where it mass controlled a bunch of Pokemon but it was amped by technology and it only affected Pokemon. Not sure why it couldn't affect people. If you think about it logically, it would be more beneficial for Team Rocket to use Drowzee to take direct control of the trainers since they could still get the Pokemon and eliminate a potential threat. It could be because Butch+Cassidy are also kind of stupid but maybe some Psychic Pokemon have defined limits on who and what they can control.