The light bar is visible from the front, through the touch pad. This does not matter at all for games. It helps slightly: 1) making sure the controller is charging 2) making sure the controller is connected at the start of a play session
The way the controller communicates when connected via USB has changed, but I'm not sure how. I think now it works the way you would expect - the radio is turned off and commands are passed bidirectionally over USB, and that wasn't the case before, but I'm not exactly sure.
PS4 controller has a gyroscope and a touchpad that the Xbox One controller does not have, and a whole lot less battery life, about half, as compared to the Xbox One controller.
I would rather have the battery life as multi-platform games, which is most of them, can't use the touchpad or gyroscope because of least common denominator. PS4 exclusive games will usually use both the touchpad and gyro, but they don't make a huge difference for gameplay.
When I bought the Pro is was $400 for the Pro and $300 for the Slim + a game I don't want.
Now you could consider purchasing the Slim during this special sale because the price gap is big enough. You could get half a switch for that price difference.
Lowering price increases demand! News at 11.