Computers today are easier to build, although they do have more parts to deal with (GPU power, multiple fans, RGB, etc). But it terms of technical knowledge, I think you needed a bit more in the past. Setting jumpers was a thing. 5 1/4 external bays were a thing (CD/DVD, ZIP/tape drives). IRQ conflicts was a thing (you had to plan out where to put your expansion cards). Expansion cards were a thing (personally I've used sound cards, midi daughter cards, dial-up modems, add-in network cards, RAID cards, SCSI controllers). Serial ports, parallel ports and game ports for joysticks (these were eventually added to many sound cards). When was the last time you were buying a video card based on its 2D performance? How many floppy disks was your OS install on?
And then there is the software side...I probably rebooted older computers more times a day trying to tweak a few extra KB of free memory (himem.sys anyone?) that I reboot now in a year.
I think there is a decent amount to consider if you are building a system today to go "all out", but it's very hard to build a system that just won't work at all today, especially with all of the online resources - The two "gotchas" might be RAM type (DDR4 vs DDR5) and platform (AND vs Intel), but a bit of reading and/or using a system builder site will solve that.