With a range of 0 to -100 and 0 being excellent, one would think that standing next to the source would yield a result close to 0. I haven’t tried it using a separate wifi router, but my impression is these combo units with wifi are lacking.
This is the problem so many people just immediately think that the ISP devices are inferior. This used to be the case but now that the cost of the microwave amplifiers has dropped it does not save much if anything to use low power units. Almost all units put out very close to the legally allowed power output.
You can never trust people opinions or even many of the reviews. This most times is not scientifically tested. The good news is all wifi stuff must have a FCCID. This lets you read the testing reports they are required to file with the government. They are not simple to read because there is not just one simple power limit, it depends on how wide the channel is and if you are using features like mimo or beam steering.
But if you spend any time comparing just a few you will find there is not a lot of difference between the better brand of routers and many of the ISP ones.
This is one of the fcc reports for your router there are mulitple.
https://fccid.io/XCNDVW32C/Test-Report/Test-Report-2441956
The problems with wifi tend to not be the router it the end devices that cause most the problems. Unlike a router that uses electical power from the wall and physical size is not a issue things like phones and even laptops will scarifice transmit power to save on battery or use smaller antenna. If you really dig you can find the transmit power levels for any device once you get the fccid.