Just like millennia means several thousand years, yet BioWare uses it to refer to things happening in the last 1300. It'd be a double standard to not apply that to "centuries".
My points were that Revan's influencing the Emperor to seek peace with the Republic was an accumulative effect that paid off after the Dread Masters were imprisoned. Likewise, Revan's ability to influence the Emperor came not through outright mental war, but subtle influence in critical moments of distraction. That's supported by fact, and you even agreed with me on the former.
The idea that the Dread Masters' presence changes that is pure speculation on your part. We know that they weren't prying into Revan's mind all the time, so yes, the whole "influence during moments of distraction" thing stands.
If Revan knew about the Eternal Empire he would have told the Strike Team about it on Yavin. He clearly had no idea.
And yeah, Revan taking advantage of moments when Vitiate was focusing on other things (probably Zakuul) doesn't remotely suggest they were comparable. Revan had nothing else to do but fight Vitiate's mind, while Vitiate was juggling a lot of balls at once.