MacOS had more screen sizes to target in 2011 than the iPad does today; in any case, Apple has always tolerated having iPad apps that are blown-up phone apps. Mouse support for iPad apps has existed as an accessibility feature before it was deemed a core feature. Even that isn't any kind of technological leap, mouse support has been part of Android for at least 15 years now.
None of these really explain the sloppiness and unfocused nature of Apple software, which has been best-in-class until recently.
Except those iPad apps also have to have a Web app now, and if you don't have a custom MacOS app your iPad app has to look good when run in MacOS. You then have to support all iPhone models. But also maybe Windows and probably Android. 25 years ago you could slap "IBM PC Compatible" on software and basically design for like 5 color depths and maybe a few resolutions.
Update cycles were on the order of a year, not a week (which also means all new features need to be ported to all the platforms above in that timeframe). Not even mentioning the backend infrastructure and maintenance to run and sync all of these when 25 years ago everything was on your local hard drive and maybe a floppy disk or CD-R.
None of these really explain the sloppiness and unfocused nature of Apple software, which has been best-in-class until recently.