I've had good success with tracking tool tests and resistFingerprinting. Granted, I usually use it with uMatrix/NoScript most of the time which cuts down on the available data a lot and maybe makes it an unfair test. One issue, I expect, is simply not enough people using resist fingerprinting to add variation to the mix. Since it's off by default, and only a small % of users use Firefox and an even tinier percentage use resistFingerprinting, unlike your example of Tor where probably most people on the tor network use the tor browser, it's likely that simply blocking things is a fingerprint all on its own. The solution there would be to get more people using it :)

I will say one downside to using it is far more bot detection websites freaking out over generic information being returned to them, causing some sites to break (some of their settings breaking webgl games too due to low values). Using a different profile avoids this, or explicitly whitelisting certain sites in privacy.resistFingerprinting.exemptedDomains - obviously if a site is using a generic tracking service for bot detection, that kills a fair amount of the benefit of the flag, so a separate profile might be best. I wish firefox had a container option for this.

... and. not too sure what you mean by changing window size on a non-standardised device. They do try to ensure the window sizes are at standard intervals, as if they were fullscreened at typical widths to reduce fingerprinting, but surely that applies to using Tor too? I mean, people don't use Tor on dedicated monitors at standard sizes.