If it's a question/competition of dominance, there's NO WAY exeggutor doesn't even get a mention. There's literally no other pokemon that's unquestionably top 5 in two gens other than lax/ttar.
And if we were using the historical argument for blissey, then exeggutor needs to have the historical argument for its gen 3 showing. In any case, Exeggutor in either RBY or GSC dominated more than blissey/forretress/dragonite in any gen (there's a case for gen 4 dnite).
The way I see it, something with a top 3 showing even in one generation exhibits more "dominance" than something that's consistently mediocre throughout.