The difference in countries counting method, geography, demographics, measures taken, regional effect makes it pretty useless. All it does is giving an indication of the alert level. Not entirely meaningless I agree, but it's way too vague.
I'm not trying to argue that it's a statistic with a lot of meaning just by itself. I don't think it is, for all the reasons you've mentioned.
But, it's one of the only metrics we really have to compare different countries in terms of hard results.
With that in mind, it isn't supposed to be used as some sort of pissing contest. It's just a gauge for "This country seems to have been doing a little better" and then taking the next step and asking "Why is that?" The difference could just be due to things like public transportation, population density, and so on. It could also be because they are testing better, and mitigating the spread of the virus, which is leading to fewer people dying. It could even be because they are being dishonest with their data. I think all of these things factor in.
The key here is not to just look strictly at those values. That's ridiculous. But if one country is really high in per capita deaths, and another is really low, I think it's worth looking at why that is the case.
Like you said, and I think it is worth repeating(in fact, I'd reiterate it a lot), there are a lot of other factors. Maybe a country is considering a COVID-19 death differently than another, so they just have more or less deaths as a result of that.
But, that's probably still going to be less variable than case numbers, which are so heavily influenced by how much testing you're do, and whether you're trying to test anyone and everyone, or you're only testing severe symptoms, and so on. Which is all also important data, but I think it varies more country to country. I do think some countries are just untrustworthy in terms of data, so I'd ignore them outright.
There really is no data that isn't susceptible to variations from country to country, so I think we need to use what data we have, and try to pull the meaningful aspects of it out.