There is nothing that requires an SSD to run. Nothing. That makes it optional.
Not saying it is a bad thing, but to say they are required, or essential is simply not true. That is like saying an NVidia 2080Ti is essential/required.
What you consider a big deal in performance gains is not what someone else might consider a big deal. If you play games and are on budget, then an SSD should be the last option in the list of things to get for that system. Spending more on a video card will get you more for game play.
I m really not trying to get in your face about this, but when you say things like you just said, and some inexperienced person comes along and reads it, then it could lead them to spend money on hardware they would be better off spending on a better video card, for example.
SSD's, like many higher end hardware devices, are a nice option. If you want faster boots, then that is one way to go to get there. If you want those initial load times for an application to be faster, then that is a way to get to there.
As far as overall responsiveness goes, if an SSD is making a difference in that, then the system is poorly configured. Very poorly. The thing about properly configuring a system is this; it only takes some time to do. No more cost than that.