Come on, you can't seriously take differences in visual effects as concrete evidence, given how many different, unrelated creative teams are responsible for their creation and how little systematic thought is put into them. Not to mention how many complete impossibilities are included for the sake of aesthetics, like roiling orange fireballs in the vacuum of space, ships that have bright key and fill lights in the depths of interstellar space, nebulae that are millions of times denser than real nebulae, ships that are shown to be only a few ship lengths apart when dialogue explicitly puts them thousands of kilometers apart, etc. It's impossible to take visual effects literally as concrete evidence of anything. To say warp drive is slower near planets just because the folks at ILM who did the shot of the BoP warping away from Earth made it move slowly across the screen -- I'm sorry, that's just not reasonable. It's only evidence of an inconsistency in how different artists choose to interpret the story, not of an in-universe inconsistency.