My Windows devices since 97 were consistent top of the line and rarely lasted more than 2 years before they slowed to an unbearable speed. In 2012 I switched to Mac and still use the same MacBook Pro which still runs as quick as it did 6 years ago. It was a huge investment at the time but turned out to be cheaper than the 4+ Windows machine I likely would have cycled through not to mention the boot time and performan…
I built a Windows PC using parts from MicroCenter back in 2014. Core i5-4690K, 16GB RAM, 512GB SSD, GTX 970 running Windows 8. It was around $1400 USD at that time, if I remember correctly.
It's now 2018. That same PC with all it's original hardware, is now running Windows 10 just as quickly as always. Not only is the performance still great, but my 4-year-old mid-range PC still outperforms many brand new PCs today. (It's still slightly faster than the current 21in 4K i5 iMac, for example).
If you had bought a Windows machine in 2012, it would not have "slowed down" the way your 90's computers did, and could still use it at it's full original performance today (just like your Mac).