I did some statistical evaluation since I was irked by the high number of single stagers in Gen7.

HOWEVER, percent-wise, Gen7 still lies behind Gen2 measured by its introduced single stagers. I did not take later (pre-)evos into consideration. Here are the stats:


Generation | #newPokémon (without legendaries) | #singlestage | (-later changed) ; percentage of single stage mons

Gen1: 146 - 18 (-12) ; 12,3%
Gen2: 94 - 21 (-8) ; 22,3%
Gen3: 125 - 21 (-3) ; 16,8%
Gen4: 92 - 5 ; 5,4%
Gen5: 142 - 14 ; 10%
Gen6: 62 - 5 ; 8%
Gen7: 66 - 14 ; 21,2%