The Warp 10 being infinite velocity wasn't really a bad idea, but it was ultimately executed horribly or wasn't enforced that well. Ideally, it would have simplified the warp scale, avoided cumbersome-sounding warp factors in dialogue like Warp 187.4, and still allow the Galaxy to be a fairly large place that couldn't be traveled in just a few seconds. Warp 9.1 to Warp 9.9 would have been sufficient "speed of plot" velocities with Warp 10 an unreachable velocity, something that no
vessel could really reach, no matter what. VOY's "Threshold" should simply not have happened in that light, IMO.