I do not know how prevalent memory pressure is for other users. It's been the primary reason of "sluggish computer" for me. If you know more about this topic, I'd be thrilled to hear other possible explanations beyond "it's more complicated than that".
As professionals we often forget what it is to be a casual user. Asking a casual user to learn what you explained as folklore is simply too much to ask. Everyone who uses a computer should at least be technically literate to a degree but that means understanding the basics. To a casual user the basics are: my computer has a processor that executes tasks, it has RAM that stores data for quick retrieval, and a hard disk for long term storage. Each application uses a percentage of my finite RAM and when it runs out my system slows down. Therefore logic dictates that if I kill the app taking the up the most RAM my computer will go faster.
That's all they usually know. We understand that Activity Monitor lies to us and killing random processes is voodoo but we also have to take into account how we use our machines. The casual user will be able to solve their problem by killing processes more often than people like us will because of the way they use their systems plus there is a placebo effect for them. When they kill a process they often feel like the system just got faster regardless of whether it really did.
I liken it to driving a car. Ask some random person about fuel economy. Their thinking is "high octane fuel has more energy per gallon therefore if I use it I'll get better fuel economy". They might even know the relationship between tire inflation and fuel economy too if you're lucky. Ask a professional driver about those things and they'll look down at the average person like they're crazy. They know all how octane, oil, air filtration, shocks, struts, aerodynamics, etc, etc. all contribute to better fuel economy. "If only the average driver knew what I knew, then they'd save a ton on gas" theyd think. But alas, that's too much to expect so we just have to make sure they get the basics and it's up to the professionals to provide the average person with something that just works and do our best to be one step ahead of users by anticipating their usage patterns. This applies to hardware/software engineering, car manufacturing, and anything else. You just can't expect the user to learn or even take an interest in even a quarter of what we know.
If that's you advocate, let's stop here with this discussion, as there's no common ground.
When you're having a problem, first you try to understand it in order to try to solve the root cause. Applying rules of thumb like "kill top RSS process" are as sensible as rules of thumb regarding running repair permissions, sizing paging files or hoping arbitrary herbs cure arbitrary diseases.
Activity Monitor is useless because it's impossible to assess how a specific action will affect the system. Users should understand what's going on when they kill a process and the tools should help them to do so. When people do something, they should understand it, even casual users. Activity Monitor exposes data that's not understood by most users, although it leaves the impression that it does.
Just for trivia, memory pressure, hasn't been the primary reason for "the whole system become sluggish" for a few years already.