your comment "it doesn’t matter which OS, Windows/XP, 7 or 10, or a host of light weight Linux systems. All are equally slow)" Is there better? some RISC or perhaps obscure "Solaris"? Don't get me wrong, to me the O/S is like going to a restaurant. You get to choose, tables, dine in or carry out. eat on the patio, Punch the chef in the nose. you can do plenty before you even sit or order..To get to the meat and potatoes--- the program.. and the speed you get it. depends on if it's been compiled and how good that is, or natively written in machine code, and just how many people do that these days. Not I since the 6502 days...
So given any O/S once you select the program... it runs at some speed dependent on if it's using an interperator, or how good the complier is, or if someone actually wrote it in machine language. even then how many "calls" are being made to the O/S or drivers, and so on. Then on top of all of that, what overhead is going on.....An O/S does not necessarly determine speed of a "job" or the program. Speed is determined on many factors such as the number of processes running, cache, DMA's, interrupts, swap space, and who the programmer was and how he attacked and solved the programming task.
That's why the lowly ARDUINO works as well as it does, there is no O/S only machine language code running. Now it still can be tweaked by the quality of the compiler, and the programmers ability. to write the coding structure for efficient execution.
Back in the day of my 1st programming class at Henry Ford College maybe 1968, the instructor gave us a programming problem an engineering drawing of a block with various holes drilled in it. We were given a 2x4x4 piece of wood and loaded it into a NC drill press and ran our paper tape. You passed if you drilled the holes, right number in the right place, at the right depth...The instructor had a go-no go gauge that verified location and depth of holes. That was Pass-FAIL. Go-no GO. If Go,Your grade was determined by the instructor pinning the paper tape to the wall and who had the shortest paper tape..got the highest grade.. One gal had a paper tape twice as long as everyone else but by the GO-NO go guage she passed. She had no idea as to how to be productive.
So to me the O/s is an evil necessity in order to load, execute, move, copy, delete or save a program. Some early O/S's like CP/M and DOS batch, that's about all you could do.. old guys well know the program pip...