I prefer a 10 point scale; anything less than that is just too vague, and anything more is too arbitrary. A 3/5 for example doesn’t really tell me anything. It could be the equivalent of a 5/10, in which case the game would be pretty meh, or it could be the equivalent of a 7/10, which means the game is pretty decent.
Regarding the issue that the lower half of a 10 point (or 100 point) scale is rarely used, I think that‘s mostly due to the fact that there are very few games these days (especially in the AAA space) that are genuinely terrible. It seems people have forgotten just how absolutely shitty and downright unplayable some games in the past used to be. Like, there aren’t really any modern equivalents to abominations like ET or Superman 64 for example, at least none that I can think of. I remember seeing quite a few scores below 5/10 (or 50/100) in gaming magazines during the 32-bit era (when I first started reading them); those kinds of scores got rarer during the PS2 era, and then almost vanished starting with 7th gen. And I think that’s because games on average have gotten much better since then.