I personally disagree and fully believe feeding a potion to someone should be a counted action as an "action [that] cannot actually be performed for reasons of safety or reality but must be considered as taking some time to complete" especially since it is an interaction with another player that isn't performing any pantomime that should be 1. announced to that player for clear comprehension of what is occuring since it is NOT happening in reality and 2. be interruptible by that player (if they're conscious, etc.) or other players as per standard interruptible means, since they are delivering an in-game effect to another player and it is very frequently an action taking place in active combat.
According to your logic, I can tell someone to close their eyes in-game while they are fully conscious, hold a vial silently vaguely in the area near their head for 3 seconds while they sit there, then say "Aha, I just fed you a Paralysis potion, even though you definitely would have been able to tell that was happening in real life if I actually was opening your mouth and pouring liquid inside!"
If an action doesn't affect anyone but myself, sure, I'll absolutely pantomine and l don't count it. But if it does affect someone else and they're not in on the pantomime, I should count it so that everyone involved or witnessing the action is in the loop of what is happening.
When I drink a potion myself, I pantomime all actions involved: lift potion, open mouth, make drinking motion, etc. When I feed a potion to someone else, I can't make them do the pantomime parts involved on their part - only the pantomime on my part. They aren't doing anything. Therefore, the action isn't taking place in reality and should fall under 3-count purview.
I can speak with 100% certainty that there are several known chapters, past and present, including those overseen/played by members of ARC past and present, that have played by the paradigm I describe above at every game for 15+ years. I know there are members of every single National committee (including ARC) that currently that do this because they believe it to be the proper method and how it is done in the chapters they play. It's a long-lived, widespread thing. To those chapters/players, the change being made here is just as notable of a "very big rules change to an existing mechanic to suddenly add" in the other direction and is set to be a very confusing shift for a lot of players. It's been an ambiguous thing for a long time played differently across the country, and I don't think it can be simply determined in the rulebook as one way or the other without going through proper Rules discussion and approval channels.
But hey, I'm not the one writing the rulebook, so my opinion doesn't matter.