There is a difference though. Say for instance a 6 in Dex gets you one attack, 12 gets you 2 and 18 gets you 3 attacks. Now any Dex from 7-11 and 13-17 is a waste of points since it gets you nothing tangible. Currently in RTwP every single point of Dex does something. With multiple attacks per action it creates the break points issue people have been mentioning. Plus multiple attacks in a single action begins to throw the action economy out of whack if you can exploit it.
This is a good point. But even the old BG games had half attacks per round. You could have 2 or 2.5 attacks per round. So one round you get 2 attacks, the next round get 3 attacks, etc. That mitigates the break point issue to some degree, but it will still exist. The question is, does it matter? As long as the gameplay is fun and you can make the type of characters you want (fast ones, slow ones, tank ones, etc).
That being said, if the FFX method of having "turns" but not "rounds" is something that can be implemented while preserving the pre-existing rules/stats, that does seem like a more elegant solution. I just echo what someone above me said: it seems like such an obvious solution that I wonder if there was some huge barrier to implementing it from the start.