I think you can get far more power then you ever need in some high end systems, for the majority of gaming and computing needs a relatively modest system can more then suffice.
That said I have been watching my boy play Detroit Become Human all day, and that's visually stunning running on a PS4 - which as we know isn't exactly the highest spec.
i agree totally. my mid range / enthusiast system is more than capable of running all the games i have at max settings at above 60fps. but like some other systems/setups, who run triple monitor setups, will need that extra performance. and if you want a higher frame rate / ''smoother look'' (i say that loosely) you again will need higher grade hardware.
i suppose for gamers, it really depends on how much you want to immerse yourself in them. and you are right, for the majority, a mid tier PC is more than enough, but for those select few, they want to have the best experience possible. but that will come with the issues mentioned when it comes to maintenance, trouble shooting and upgrading.