Okay, let's look at this purely from the number of unique moulds then.
Autobots = 9*/33 or 27% have been done as MPs
Decepticons = 7**/18 or 39% have been done as MPs
So when we only look at the unique moulds, the Decepticons still proportionately fare better than the Autobots.
If we don't adjust figures proportionately then this would actually skew facts -- it'd be like saying that Japan has more unemployed people (4.6M) than Australia without adjusting for population (1.3M). But of course, Japan has a population of 127M people whereas Australia has 23M, so rather than looking at unemployment numbers we look at unemployment rates which are proportionate to the population. Japan's unemployment rate is 3.2% whereas Australia's is nearly double that at 5.7% of our population.
Similarly yes, there are 9 unique Autobot moulds vs 7 unique Decepticon moulds. But when we make adjustments relative to the number of unique Decepticon moulds available from the early G1 run, then proportionately speaking things actually look better for the Decepticons. Even if TakaraTOMY were to release the rest of the early G1 figures as MPs, the Autobots would still outnumber the Decepticons. It's simply because there is simply a larger pool of Autobots to draw from to make MP products out of than Decepticons. TakaraTOMY can't exactly travel back in time and convince Hasbro to create more Decepticons back in 1984-85.
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*Autobot unique moulds
Optimus Prime
Bluestreak/Prowl/Smokescreen
Jazz
Hound
Ironhide/Ratchet
Mirage
Sideswipe
Sunstreaker
Trailbreaker/Hoist
Wheeljack
Brawn
Bumblebee
Cliffjumper
Gears
Huffer
Windcharger
Jetfire
Omega Supreme
Blaster
Grapple/Inferno
Skids
Tracks
Perceptor
Beachcomber
Cosmos
Powerglide
Seaspray
Warpath
Grimlock
Slag
Sludge
Snarl
Swoop
**Decepticon unique moulds
Megatron
Soundwave
Buzzsaw/Laserbeak
Frenzy/Rumble
Ravage
Skywarp/Starscream/Thundercracker/Dirge/Ramjet/Thrust
Shockwave
Astrotrain
Blitzwing
Bombshell
Kickback
Shrapnel
Bonecrusher
Long Haul
Hook
Mixmaster
Scavenger
Scrapper