Ripple had limitations. It's primary usage was in fighting vampires due to the whole Sunlight Overdrive thingamajig. Even then, if Araki had focused only on Ripple, either this would have had to have hit impossibly ridiculous levels of physical power (DBZ) or he'd have plateaued in power levels.
Stands allowed him to both have the Stand Users fight other human beings with Stands at relatively equal levels and have no limit to power levels since Stand powers are pretty much ANY batshit insane power you can think of.
Speaking of which, I need to watch Law of Ueki.