Thinking back to the early iPads I used- they were very useful for travelling/commuting,
weighing very little but with a screen that was massive compared to phones. Also, a lot of websites were still horribly optimised for mobile use, and the iPad was much better for browsing the internet than the iPhones were. It could replace the desktop/laptop for browsing, light gaming, editing photos, etc. The iPad 3 also brought an excellent screen that was much nicer than the Macs of the day.
Fast forward 11/12 years and the internet is well optimised for phones, phone screens are far larger, phones are much faster, and I haven't even bothered to use my current iPad once this year. The phone caught up, while the iPad continued to lag behind the Mac for productivity, while Mac screens kinda caught up.