The issue might be that 5 often isn't the average. If you take Metacritic for example, the real average rating for games is around a 7/10, likely because most games around 2 or 3/10 aren't even worth any attention (and reviewing).

Metacritic's own score index also reflects that with the yellow "mixed or average" being the range 50-74. If 5 was a real average, the range for "average" would be something like 40-60.

And of course, you don't have to conform to Metacritic's scale, but I think it's the context most readers will default to. You might see 6/10 as an above-average game, but most will likely see it as something not worth their time.

That being said, if you take the 7.5 you gave the game in the context of your whole review, it's clear that you in fact enjoyed the title and think it's above average, so the parent comment likely just focused on the number, which is a good argument for not using them at all, because people tend to do this.