That would be true for the 4090, but the 3090 is even more cut down so the 5090 is about 100% faster in rasterization (based on the 4090 being nearly 70% faster than the 3090 and the 5090 being approx 25% faster than the 4090)

The increase from a 3090 to a 5090 would be way more than that.

Certainly worth paying +$1k if you are doing anything that requires GPU power (hash cracking with hashcat for example)