I still have my original iPad. Actually, my brother has it, as I loaned it to him to read a book that's on it. It's amazing how well it's held up. I used that a ton when I was studying, researching and taking notes in the library, etc.
[what studying used to look like for me in 2013]
I tried to replace it with an iPad mini 2. I wanted to love it so much, and I still do. The iPad mini looks so cool! The only place it ever made any sense though, was when I used to catch the train (45 min each way) to work. I spent most of my time with it being annoyed by the small screen, and replaced it with the iPad Air 2 that I'm still using. I'm badly overdue for an upgrade, it doesn't do half of what I want it to any more, and the battery life is terrible, but I can't afford to get another iPad right now. As much as I desperately want a 13" iPad Air, I think I will be lucky if I can save up to get the next iteration of the base model.
I've played iPads, deployed them, had them available to use daily, but just don't. It has never been an attractive product to me, and that is simply because I'd rather have a clamshell or phone. They're better than ever, but I still haven't found a place where it is a better option than MacBook or iPhone aside from maybe the battery life.
If you're evaluating an iPad on an equivalent footing to a MacBook, I'm not surprised. While a great many people have had success and enjoyment using an iPad instead of a MacBook, one of the key strengths of the iPad is as a companion device. A MacBook + iPad is an unbeatable combination for me, and I'm still using my iPad Air 2, so I don't have access to any of the things that make the combination really great!
Sometimes there are tasks where it is just better to hold the screen and use your fingers. For me, that is when I am working as a draftsman, reading markups from designers or engineers. I could, and often have, put the PDFs on a second screen to read as I modify my drawings, but I find I make fewer mistakes and omissions if I have that PDF on my iPad, and use the annotation tools to mark what I've done. Holding the iPad, zooming and dragging the PDF, make it easier to do my job.
The other area an iPad is unbeatable in for me is when I'm playing bass. Putting my iPad on a music stand to display my sheet music/chord charts, while I use a BT foot pedal to turn pages, can't be replaced with a laptop or phone.