DLSS is always relevant if the GPU utilization is reaching 100% / close to it, in games with DLSS off. I know it doesn't appeal to everyone, but it's a very easy way to boost performance, whilst keeping the benefits of a higher output resolution.
The only obvious drawback, is quite a lot of recently released games don't support it. There are still games that fully utilize a RTX 3090 at high resolutions, so anything that help to reduce the load on the GPU is an obvious benefit. If Flight Simulator (highly GPU intensive) had DLSS, I'm sure the RTX 3090 could handle it at high framerates, at 4K.
I notice many reviews seem to ignore DLSS, to try to give a fairer view of AMD and Nvidia GPUs. But, I don't think this gives a realistic view of performance for many games (when you compare many games at 4K, with DLSS most RTX 3000 series cards can generally hit 60 FPS or more at 4K, equivalent AMD cards often cannot). It does seem strange to me that some still debate the effectiveness of DLSS, I can only guess this is a case of "The Fox and the Grapes".
Having said that, perhaps AMD will be able to develop an equivalent technology to DLSS this year, at which point, I think the RX 6800 XT and RX 6900 will become a much more attractive choice. Although, there may be even better GPUs from AMD coming next year, so maybe not the best time to buy, with the supply situation as it is.