Sure just look at amds own technical info and their timescales, games with dlss added already improves the delivery time. If only amd got on board with the open source solution streamline which would have allowed devs to integrate all 3, amd probably wouldn't have struggled with FSR 2 uptake and now FSR 3 uptake.
But the reality is whilst they are quick to add, the biggest problem is that with fsr, as even stated in the interview between DF and amd and as per their own documentation, to get the best results from FSR, it is up to the devs to tune it, where as with dlss, it's mostly just plug in and of you go and pick a preset (hence why with dlss, we can swap out files and change presets ourselves where as with fsr, you can't), this is one of the reasons why fsr is so hit and miss (and more miss) outside of amd technically sponsored titles especially for presets less than UQ/Q and at resolutions lower than 4k.
As shown in the past with previous nvidia methods, nvidia could very easily lock out fsr if they wanted but it would cause a huge backfire and not be in anyones interest including theirs.