The thing to remember, is what slows down PC's during start-up so much, is all the useless crap put on the operating system, both by the PC manufacturer, and by the user.
Even with a hard drive (versus SSD), a fresh install of Windows is blazing fast. But once you add on all the stuff you let run in the background, it ties up resources, and slows it down. Depending on the system specs, and the operating system used, it can get worse.
I once was asked to look at a computer that belonged to a friend of a friend, and see if I could speed it up. This was in the early days of Vista, when PC manufacturers were putting it on systems it had no right to be on. The system in question was an Athlon 1.3GHz, with 512mb of PC-133 ram. When it finally got the O/S loaded, and up on the desktop (20 minutes later), the taskbar was literally more than half way across the screen! 😵
To make matters worse, it was a strange type of ram that the manufacturer used on the motherboard, and buying another 512mb stick was going to cost over $100. I told my friend to tell the guy to reinstall Windows, then sell it, and buy something with better specs! 🙄