Sorry that's just not possible. There are gamer targeted systems that are better specs than anything apple ever made (even after market upgrades) in the sun $2k range.
The problem is, they don't run macOS. And if your whole work-environment is centered around macOS, it is not an easy choice to leave that behind, and consequently, hardware upgrades don't come cheap.
No, if he wants to be a replacement, one has to assume he wants to be compatible and keep using the applications he currently uses. Any non-Mac system might be an "alternative" but not a "replacement".
The problem is with changing the software environment. Most applications are not available on all operation systems. So your hunt starts for solutions where the application is not available on other operation systems.
I'm in the middle of producing a 17 song concept album. If I switch platforms, I have to completely redo all my mixes and learn a whole lot of new tooling. What's the cost of that? Dozens of hours of my time...
>There are gamer targeted systems that are better specs than anything apple ever made
Which is irrelevant. I don't a "gamer system". I want thin, light, excellent construction, and good battery life, great trackpad, and a good enough CPU/GPU to achieve all that.
Comparable Mac and PC systems for that cost $2000 and way up...