Let’s put it like this....
you have a 4790k and a 1070.
someone offers you a full platform upgrade to say a 5900x or a 3070...which one would you take assuming you couldn’t sell it?
it’s a complete no brainer. The extra £800+ outlay of the new platform would be nearly double the GPU outlay for much less gaming benefit. Even if you just said 5600x it’s still £500+.
I just don’t see the essential nature of moving from a 4790k. Very desirable yes, necessary and worth the money...not really otherwise I would have done it by now.
Averages will go up sure, but lows wont improve much. 6fps lows vs 40fps lows on my very same gpu due to swapping the cpu out. Thats a 6.5x increase on the lows (1070 to 2070s) as well as 10-15% increase in averages compared to a less than 30% difference on the averages (going 2070s to 3070) as it wont be hitting the full 30% benchmarks sites say it will if i kept a 4790k. So i could keep the 4790k, get an estimated 20-25% avg boost and still have bad lows and stuttering, or i could keep the 2070s and remove the lows and stuttering and get a 10-15% boost to averages. Not to mention the overall system speed benefits, nvme support, halving the encoding times etc.
Thats the point i was at and with that choice, the gaming difference between a system upgrade (£300 cpu, £60 ram and £150 mobo) vs a 3070 (£600-650) is a much closer call than you're making it out to be.