The question posed in the headline is merely rhetorical: of course outlines aren't uncool. In fact, conducting a deposition without an outline would be a lot like jumping out of an airplane without a parachute.
A related question is how much detail your outline should include. If you're new to the deposition process, your outline should include lots of detail, as this humble post by The Uncivil Litigator makes clear. It means your outline should include not only issues and topics, but many actual questions. Just remember never to become wedded to an outline: to follow up properly on the witness's answers, you have to look away from your outline and listen.
As you become more comfortable with the deposition process, your outline might include only a checklist of issues you want to cover, one that you've prepared ahead of time after carefully thinking about the goals of the deposition in the context of the particular case. But to walk into a deposition without at least this level of preparation? Do it only if you want to risk showing up on the first day of trial and going splat.