You mean between Gens 2 and 4 and Gens 1, 3, and 5? Because there's no "happy medium" there, there's literally only 7 more Pokemon in Gen 4 than Gen 2.
If that is what you mean, I agree. I'm sick of every generation falling into this stupid trend of "lots of new Pokemon, little to no new evolutions in odd gens, fewer new Pokemon, tons of new evolutions in even gens", it really gets annoying. For instance, let's say a new Pokemon gets revealed in 6th gen that just really sucks and needs a new evolution. Under this pattern, it won't get one until 8th gen. Likewise, let's say we find that there's a lack of balance 7th gen and we need more Pokemon of a particular type. With the limited amount of new families offered in even gens, 8th gen won't be able to fix this. I think they should just add whatever's necessary when it's necessary.