AMD platforms tend to have longer lifespans than Intel. So while they may be 5% Intel platforms in performance, with BIOS updates you can expect an AMD based system to last 5+ years with incremental upgrades to CPU, RAM, and GFX.
It is worth noting the comment above "The other thing to bear in mind is we're nearing the end of the pcie 4.0/DDR4 generation. AMD is releasing Ryzen 3.0 next month, which is their last cpu on the current platform. Ryzen 4.0 (or whatever its called) will need a new mobo and memory" but with everything in the PC world, the next big thing is always just a few months away and you can spend a lifetime waiting for the 'right time' to buy. I purchased my system in March this year, and with the release of Nvidia RTX graphics cards and AMD Big Navi, I am already a generation behind. But I'm still playing games at maxed out settings (only 1080p rather than 4k however) including Flight Sim 2020, Star Wars: Squadrons, and Battlefield 5 at 75 frames per second, as I have freesync enabled.
For reference, I moved to my current system from an AMD AM2 Phenom X4 DDR2 system that had lasted me about a decade, with iterative upgrades to the CPU, increasing RAM, adding SSD drives, and changing the graphics card every 3 years. I only really upgraded as new titles were no longer supported by the CPU instructions.
Ryzen 4.0 may be a year away, and it depends if you want to sit with what you have or wait a year? You can get plenty of great gaming done in that year, and once Ryzen 4.0 is released, there will still be another 'next big thing' six months away.
