All your points have merit. Understand your point if Apple had no such app for any device. Apple has one for the iPhone. Already made, works every time, all the benefits of Apple. A five minute job to convert the iPhone app to iPad. Plus consistency in use a big factor. I have tried a good number of iPad calculator apps. Most suffer from ads and required upgrades. Several do not work at all. I will try PCalc. Thanks for that tip.
It would be considerably more than five minutes to convert the iPhone app to the iPad. And consistency loses out big time if they port the exact same app over - the iPhone's calculator app has buttons that are, very roughly, the size of a thumb. What happens if you port that app directly to the iPad? Either you end up with a same-sized calculator screen, swimming in an ocean of blank screen, or you enlarge it to the full screen, and, well...
... the iPad 13 Mini's screen is roughly 2-1/4" wide. That puts 4 calculator buttons across at about 9/16" wide each. Reasonable for human fingers. The 12.9" iPad Pro's screen is roughly 7-3/4" wide. That puts 4 calculator buttons across at about 2" wide each (closer to 1-15/16").
That's only reasonable for fingers
if you're a silverback gorilla. A human can't reasonably "type" on that. So, you can't just scale up the existing app (an Android vendor might ship that, Apple won't). If you don't just scale it up, suddenly you're left with design decisions - what to do with all the extra screen space? Lots more buttons (what will they do)? Big scrolling list of previous calculations? All of this is a considerable departure from the iPhone's calculator app. It's not a five minute job to convert (and trust me, even with no changes at all, it was never a five minute job), unless you want an app that objectively sucks. Then all the people complaining that there wasn't a built-in calculator app would simply switch straight away to complaining that the built-in app sucks, and laughing at Apple for shipping it with gorilla-sized buttons.
(There's a philosophical argument too - so, if Apple made a total knockout calculator for the iPad that used all that extra screen space for scientific / financial calculator buttons and a scrolling tape of previous answers - and, I suspect Apple would actually want to go in a more disruptive direction of not simply aping historical calculator designs but reinventing it somehow - then... what happens to the
iPhone Calculator app? It doesn't have space on screen for all that extra stuff. You're left with either inventing ways of layering in multiple sets of buttons to accommodate much more functionality on the iPhone screen, ending up with a calculator that's likely more difficult to use for the basic functions for which it was originally designed, or... you ship new wonder-calculator with the iPad and leave the iPhone with the dinky old 4-function calculator, and then people will complain that the iPhone is now being left behind. I have a feeling this may be another reason Apple has never done anything with an iPad calculator. And, for what it's worth, PCalc on the iPhone can be set up so that in portrait mode you get a slightly more powerful calculator, and then if you rotate to landscape mode, you get a full-blown scientific calculator - which is super cool, but more complex than Apple would want to present to the average grandmother who just wants to add some numbers. Personally, I also have PCalc set to use RPN entry in both modes, because as a programmer I find that more intuitive and powerful, though most people would find it confusing.)
All that aside, yes, try PCalc. It's a great app. I don't know if there's a trial mode these days, but there is a PCalc lite that will give you an idea how it works (I expect the full blown version is substantially better). If you like it, get the full-blown version (as opposed to upgrading the lite version). It's possibly not the best calculator ever, but it's a good solid app, the full version has no ads, it's well supported, and has a long history (going back to pre-OSX Macs).