Rubbish.
The 5090 is 30% faster at most, which isn't enough to suddenly not need DLSS and/or FG. You'll get a bit more performance out of a 5090 with the same settings but nothing that will make a massive difference to the experience.
For the record I get about 75fps average with path tracing and DLSS Quality on my 34" ultrawide which is more than adequate. Not everyone games at 4K and needs 200fps all the time.
It is 45-50fps with dlss quality at 4k ATM, some drops to low 40s at time. FG necessary with 4090. Can probably get away with no FG with a 5090.