That really is inexcusable, as mentioned push it up the chain.
I could see you having genuine problems if you used the system to its maximum potential, especially in hot weather depending on where you're situated/ac availability etc. The 9950X3D isn't the heat monster something like a 14900K can be, but it's still capable of generating a good chunk when strained and the 5090 is ridiculous all by itself with an almost 600W tdp. You should not have to do a DIY fix for a system at that spec and price range, and as mentioned they may make a fuss about warranty if you do.
If you haven't already, I'd set a power limit on your GPU of 450W, it'll improve temps/boosting and reduce the chances if any issues with the 12VHPWR connection. I recommend this to anyone buying a 5090 regardless of situation mind you.
I'd also argue they've skimped on the PSU for that rig, as expected. The Corsair RME range was always their budget modular PSU, but they actually changed OEM a year or so back and there was a notable decline in the quality. While I don't think it'd die and kill any components, I wouldn't choose it personally and would expect it to struggle more in high temps than the sort of 1000W range supplies I'd personally include in a rig of that calibre, and they've absolutely ensured with that placement it'll reach very high temps under high load.
There's also the poor cable management as mentioned by
@pastymuncher too, I would be forgiving if spending half that on a PC but far more critical going up the expense chain, you've bought a PC equivalent of a super car and as such should rightfully expect a much better product.