From what I saw back in the '80s', humans had a 'third-level effector intelligence' (what effector even meant, in that context, I don't know), and each 'level' afterwards was supposed to be an order of magnitude 'smarter' (in terms of processing power and memory storage, I would assume, since there's no real way to measure 'intelligence' at present in other terms, 'intelligence' being kind of squishily defined and often misinterpreted). Kryptonians, like Superman, had a fifth level 'effector' intelligence, meaning that they where, as a race, *100 times smarter* than humans. (As a race who, at maximum potential, could think and react near light-speed, and may have had their entire races culture, history, science, etc. downloaded into their brains, at some point, like baby Kal-El, who grew up on a farm in Kansas, but still able to create alien technology like the 'Super-Mobile' in seconds.)
A standard Coluan had a 10th level effector intelligence, making them five orders of magnitude 'smarter' than Superman (which, again, might only have represented their increased processing power and memory storage, since the scale seemed to be a Coluan scale, and probably had zero measurements for stuff like 'social intelligence' or artistic ability), while Brainy himself was a 12 on what the rest of Colu thought of as a scale-to-10 (with themselves at the top), making him, by Coluan measurements, 100 times 'smarter' than the average Coluan.
None of the other races were, that I know of, even measured on this scale, but I don't see any reason why Bgtzlns or Winathians or Braalians or Titanians or Naltorians or Carggites or Trommites, etc., who seem basically human in both physiology and, for the most part, psychology and behaviors, would be any smarter (or dumber) than Earth-humans. Similarly, aliens like Blok and Tellus and Chameleon Boy don't seem superhumanly smart (or more than normally 'dense' in the case of Blok), although Cham is certainly smart within the normal range of 'human-smart' (as are Nura and Imra).
Outliers;
1) Mon-El should be as smart as Superman, but has never been shown to be able to make super-science gizmos the way Superman has, nor did Universo seem to consider him one of the four smartest Legionnaires (along with Querl, Imra, Reep and Nura).
2) In the Threeboot, someone quips that Brainy said humans are a fifth level intelligence and Brainy snaps back, 'I said that humanity,
as a species, is a fifth level intelligence,' which makes no sense and I'm just going to ignore.
I'd be inclined to veer away from trying to use these numbers in a game, as anything other than data points, just as actual IQ scores aren't anything other than benchmarks for the Intelligence attributes in games (or how much weight you can lift or how fast you can run in KM aren't used as literal attribute numbers to represent a characters Strength or Speed). What I feel that the effector intelligence scale does represent is that Brainy can remember a million times more precise data than I can, and do math a million times more quickly, not that he's a million times 'smarter' (since, thanks to the demands of plot, and merely-human intelligence of those writing him, he can do some pretty dumb stuff).