He's right though, the last really decent upgradable Mac's were the desktop 4,1 and 5,1 series Mac Pro series.
Its more the video card being an issue than anything else, CPU's, ram and ssd speeds in Mac's are great.
The older Mac Pro's are awesome machines. I have a bunch of 4,1 and 5,1's that I've upgraded cpu's, video cards, wifi for, and they're plenty fast for gaming, especially if you want to stick a decent GFX card eg a Titan X or 980Ti in them, or R9 Fury if you like AMD (I don't). I'm less keen on gaming now though than when I was younger - a PS4, Wii U, and 3DS fill my needs.
Its ironic, when I was younger I didn't have the money for a good setup, now I do, I can't be bothered.
Only thing that might persuade me would probably be Elite Dangerous, as I've seen some great VR setups with that.
Elite has come a long way since the BBC Micro days! (Although I had it on a Spectrum, we only had Beeb's at School).