I have a confession to make. I still don't know what is the killer app or use case for an ipad.
I feel the iPad is an incredibly personal device, and what makes it "tick" will differ from user to user.
For me, the iPad excels in being everything that my laptop is not. Here are some examples.
1) Teaching in class - the apps I typically use are notability, powerpoint, the camera app, quizizz, chrome (for web-based apps). As my iPad is mirrored to an Apple TV, this frees me up to move around in class and monitor what my students are doing. In this regard, the iPad is far thinner and lighter than a conventional laptop. It still sports far better battery life than any intel-based windows laptop, is faster to unlock and apps are better optimised for touch.
Unless I know I will be needing my school laptop for some very specific task that can't be done from the iPad in class, it stays at my workstation.
2) It's a bigger iPod touch. I guess that as I age, I prefer performing more tasks on a larger display. And I do a lot of reading on my iPad, from social media (Mastodon, Reddit, Discord, Tapatalk) to reviewing teaching material (notability, files, notes, mindnode) to other work-related stuff (mail, safari, even messaging).
3) I find that the iPad excels at card games and tactical, turn-based board games. Examples include Slay the Spire, Lords of Waterdeep, Warhammer Quest (when the game was still around), Shadow Era (no longer play nowadays). For touch-based, Battleheart Legacy. I do also have a game controller and though few, titles like Grimvalor show what is possible on the iPad when the developer makes full use of its hardware. For example, I have Grimvalor on both my iPad Pro and my Nintendo switch, and performance is night and day. The iPad has a larger, more gorgeous display, better specs and promotion. This translates to smoother performance, faster loading times and more fluid and responsive gameplay overall. It's just a better experience all around.
4) It's a nice second display when I am working on my laptop. Sometimes, it streams YouTube or Twitch. Sometimes, it has content open that I refer to. Sometimes, I refer to my worksheet solutions and play something on as background noise while I mark.
The iPad is just this versatile slab of glass that becomes whatever I want it to be (within limits). It was the case back when I picked up my first iPad on 2012, it is still the case today.
Why pick the iPad over android alternatives? For me, it comes down to ecosystem and apps. My last iPad Pro was the A12x version that lasted my 6 years. Maybe there's a cheaper alternative out there, but I will argue that it's precisely because I opted for the high-end model back in 2018 that allowed me to hold on to my current iPad for as long as I did (ie: it pays off in the long run). May as well go for the best while I am at it.