Got nerd-sniped a bit thinking about analyzing this data.also, to provide some context for everyone, here's the percentage of ou mons in each gen that debuted in that gen, just to compare with gen 9:
gen 1:
13, 100% of the 13 mons in ou
gen 2:
11, ~45.8% of the 24 mons in ou
gen 3:
8, ~29.6% of the 27 mons in ou
gen 4:
21, ~42.8% of the 49 mons in ou
gen 5:
14, ~26.9% of the 52 mons in ou
gen 6:
19, ~32.7% of the 58 mons in ou
gen 7:
11, ~21.1% of the 52 mons in ou (i'm not counting totem kommo-o or battle bond regular greninja as separate mons because that's fucking stupid)
gen 8:
7, 20% of the 35 mons in ou
gen 9:
19, ~51.3% of the 37 mons in ou
so more than half of the mons in ou right now are from the current gen. percentage-wise, that's more than any other gen (gen 1 doesn't count because c'mon, that wouldn't be fair); in raw numbers, it's only beaten by gen 4. that being said, i think it's reasonable to assume that these numbers will change—the meta is still in a state of flux, and we have two dlcs to get through. when all is said and done, the raw number might be higher or lower, but it's very likely that the percentage will end up substantially lower thanks to the dlcs reintroducing old mons.
i'm not taking a position on whether this is good or bad because i genuinely don't care how many or how few new mons are ou as long as the meta is good (which i personally don't think it is right now but we're close, guys, we're really close). this is just data presented neutrally. make of it what you will
I don't think looking at simple percentage of new mons in OU is really the correct thing to look at in comparing power creep. You really want to compare the percentage of new mons in OU vs the percentage of new mons overall.
For example, in Gen 2, 45.8% of OU mons may have been from Gen 2, but only 39.8% of all mons were from that Gen. In other words, Gen 2 is overrepresented, and there was some (minor) level of powercreep.
In Gen 3, 29.6% of OU mons were Gen 3, but 35% of all mons were Gen 3. So Gen 3 is slightly weaker.
Quick table I worked up (using your numbers for % in OU).
The numbers are pretty badly off for Gens 6+, because I was lazy and just went off national dex numbers - so it's not properly accounting for Mega Evolutions or Regional Forms (or even for mons with multiple forms like Rotom).
If anyone cares enough to figure out actual numbers of Mons Added vs Total Mons the numbers could be more meaningful.
% in OU | Num of Mons Added | Total Mons | % of New Mons | % in OU / % of New Mons | |
Gen 1 | 100% | 151 | 151 | 1 | 1 |
Gen 2 | 0.458 | 100 | 251 | 0.3984063745 | 1.14958 |
Gen 3 | 0.296 | 135 | 386 | 0.3497409326 | 0.8463407407 |
Gen 4 | 0.428 | 107 | 493 | 0.2170385396 | 1.972 |
Gen 5 | 0.269 | 156 | 649 | 0.2403697997 | 1.119108974 |
Gen 6 | 0.327 | 72 | 721 | 0.09986130374 | 3.274541667 |
Gen 7 | 0.211 | 88 | 809 | 0.108776267 | 1.939761364 |
Gen 8 | 0.2 | 89 | 664 | 0.1340361446 | 1.492134831 |
Gen 9 | 0.513 | 112 | 478 | 0.2343096234 | 2.189410714 |