That's weird, usually I've seen 6 and 7 included in the "Unplayable junk" category, with 8 as "Average", 9 as "Pretty good", and 10 as "Best, except somehow also the baseline expectation"
As for how many Sonic games fit into the 1-7 range, it's basically all the ones where they tried to half-ass a new playstyle that they couldn't actually pull off, and also Forces.