It is, which is why professional cameras have auto modes.
Knowing when to not use manual is a skill in itself. Those who stubbornly use it all the time in the belief they're being a better photographer are just idiots. You need to know how to use it, sure, but using at all the time is just stupid.
There's a popular local photographer who teaches beginners how to get better photographs. He teaches them that you must immediately stop using the baby auto modes, no auto exposure, full manual, no auto white balance, full manual. I sometimes meet one of his his ex-students, still struggling after years to get the exposure right, full of praise for the extraordinary skills of the master, and sure that if only they could get round to making a really determined effort to practise as much as possible they'd soon get it right.
"Knowing when to not use manual is a skill in itself"?
That "not" sounds as though you use manual most of the time, otherwise the more useful skill would be knowing when to use it.
I'm quite happy with manual. I learned my photography on manual cameras. My first DSLR had the useful innovation of a built in exposure meter and needle matching. I guess I use fully manual exposure on about 0.1% of my shots, about the same as I use one of the full auto modes. Otherwise I use a semi-auto mode, adding some exposure compensation about 50% of the time, exposure lock about 5% of the time. I do have some manual lenses which require manual focus, but otherwise I use autofocus about 90% of the time. I'm very impressed by how well my auto white balance works. I only use manual white balance (or make sure I have at least some reference white or gray in the shot) for photographing paintings, serious flower portraits, or the lighting is weird.
So for me the useful skill is knowing when to use manual, not knowing when not to use it.
