I originally bought my first iPad for my long commutes on the train--mostly for reading and gaming. I've thought about maybe commandeering the old iPad mini 3 my son doesn't use anymore and just set it up for Books and Safari.I never tried to replace my desktop or laptop with an iPad. I bought the iPad 2 for one reason only - reading manga. I was getting neck pain looking down on the laptop screen trying to read manga in bed or the couch.
I just gravitated to using the iPad more and more as both hardware and software improved. I remember back when I had the iPad 2/3, majority of websites didn't work at all on the iPad so web browsing was primarily a laptop/desktop task. Right now, there are still some sites that don't work on iPad but they've gotten a lot fewer.
Granted, I never really gave up the laptop. I just use it a lot less than before. Not a fan of huge phones. I find them too big and awkward when trying to use as phone (hard to juggle groceries and phone) while still being too small for reading, web browsing, etc. The iPads really are my Goldilocks device.
PS--do you have an Apple Watch? I've been using AnyList for groceries on my Apple Watch and it has been a GODSEND. I don't even need the phone with me--I can just check stuff off on my watch as I grab it and it live updates to my wife's phone too so she can see how far along into shopping I am and can reference the list when I call her wondering where things are.