Welcome, and congratulations as well.
You have certainly missed a fine period of Mac OS X (I came to Mac OS X on 10.4 on a Hackintosh all the way up to Snow Leopard) but macOS in its Mojave and Catalina form are not that bad either. Hardware-wise, for everyday lightweight to moderately heavy usage, you will not feel the computer slow.
I got myself a MacBook Pro 15" with dGPU (stock, top spec) in November 2011, used it lovingly till November 2016 when I added a 13" MacBook Pro with Touch Bar to my collection. Unfortunately, in a year and half, I was disenchanted with the graphics performance and the keyboard had multiple errors and I "write" for a living, so it was time for it to go. I got the top case replaced and sold it off. I was not happy with the potential repair costs when the computer would go out of warranty, and it matters to me since I keep my computers for as long as they serve my needs the way I want them to.
From the Pros, I "downgraded" to a 2017 Air. The keyboard on this feels something between the 2011 and 2016. It is good. What I like most about this is that this machine is plenty fast for my usage, and is compact enough to fit in the same space as the new 2016 did, and most importantly, I can use it without fear.
You have bought yourself a great machine that will serve you for a long time and for varied purposes, so long as you are not into constant heavy-lifting, at which point you will realise its limitations (I sometimes feel the CPU to be slightly underpowered - just sometimes). Beyond that, for everyday lightweight to moderate use, this machine is good.
The screen and colours are alright by me. Sure, the new displays are far better. But the computers with those better displays are not reliable.