So long as it's the only objective relevant metric, yes it can and more importantly has to be, or there's no point having any reviews at all.
Including scaler numbers and providing lossless material to compare them yourself can be a nice bonus, but that's it.
edit: not sure what's the english equivalent for "väännetään ratakiskosta" but anyway
You can have as many different reviews from exact same data as there are reviewers. How is that supposed to help consumers make informed choice, when one reviewer prefers one method, other some other method and so on?
That's why reviews need to stick to objective measurements, where playing field is as level as it can be. You can add toppings on that cake, like compare scalers and so on, but those are just optional toppings. Cake is necessary.
I would disagree that if we took away resolution as a metric reviews would be pointless, though that is a separate topic.
Ultimately there are 2 main features that have high correlation to performance and resolution and that is mainly transistor count and power.
As noted here:
https://forum.beyond3d.com/posts/2252880/
Upscaling techniques use less power to generate equivalent results to native, in the post above we see the different between FSR and DLSS. And we see a 20% power savings, but what about the power savings vs native? It would likely be even more. When we look at power limited scenarios, and we should, suddenly these upscaling techniques whether ML based or not matter, now more than ever. There is an obvious spectrum of power/performance between a mobile GPU to cloud computing, and somewhere in between those two endpoints is the limit of how much power and size a single desktop GPU can have. Today that is the 6900XT and the 3090. But where are we really going from this point forward? If we can have upscaling reduce our power requirements by half to generate equivalent performance at native this matters for progression in graphics.
FSR being a non ML technique saves on transistor space at the cost of having slightly more power consumption. DLSS saves on power consumption at the cost of having a higher transistor count. 2 techniques but meant to solve 2 particular problems: the need to increase die size for higher resolutions and the need to reduce power consumption to fit into the form factors we need them to.
IHVs don't care about the reviewer's abilities to benchmark, they are looking to design cards at a specific performance level within a transistor and power budget, and when FSR/DLSS/XeSS become standard technologies you may be looking at a cards where they designed it for 1440p with upscaling, or 4K with upscaling in mind, as in it's always turned on by default. The age of native is going to start going away because we're at the limits of what can fit into a desktop PC. A GPU that requires a 1000W power supply or more @ 1000 hours of play is a megawatt of power, that's significant and it's not reasonable to keep heading in that direction. Firstly, increasing transistor budgets coupled with increased clock frequencies would drive silicon costs way up, and we already feel that today. Secondly, cooling becomes increasingly difficult, there's not enough market at extreme price points to run the industry off.
The market expects performance to continue to evolve but the price must come down and that means die sizes and power consumption must come down for the market to continue to have relevant progression. Upscaling techniques must be brought into review procedures, reviewers will figure out a way to do this, it is not as difficult as IHVs going up against the hard wall of physics.