When talking about who has the best goals to games record in the league I don't think you can pick and choose, but for the sake of your argument, let's do it and we're left with:
Aguero 177 goals in
Henry 174 goals in 254 matches
Aguero 177 goals in 255 matches (3 goals more in one more match, not an identical record unless you're for some reason counting the 254 first matches of Aguero instead of calculating the average from all of his matches)
I've already said that I see what you're saying, I'm just pointing out that Aguero, no matter how you choose to do that math, is on top when it comes to goals to games.