...eh...I don't think he's totally wrong.
There is definetely a cause-effect, but it's not as extensive as, say, that one short story where they go back in time to hunt dinosaurs, and one of the guys accidentally kills a butterfly, and the modern times are we know it are completely off scale and fucked up and stuff like that. It's there, but...it's not very sensitive, from what we're shown, and as Sentenal said, that's really all that matters when wondering about things that aren't questions left by events or quotes in the games.
Apparently talking to everyone single person in past times does rather little to change anything about the present or future times, and any idea that the developers didn't show someresulting change because [insert reason here] is frankly irrelevant.
We see what we know to be Chrono Truth, beyond that we could say anything is possible, so your idea is just as viable as much of my short story; we can't say, and it really doesn't hold much ground on any argument past "What if...?"