The issue described wasn't that the underlying system couldn't support it: they were taking about native apps, which certainly had "all the APIs you need to replace Flash". The issue isn't about the runtime, it is that the Flash authoring experience itself--the app/IDE which people used to develop for Flash--was so glorious and rich in its design, and offered such wonderful affordances for making these animations, and no one has ever replicated such.
Alt reason why "Apple continues to support old hardware":
If some people found out that they NEED to get a new phone every 2 years that costs $1,000, then they might look to another cell phone manufacturer.
BTW I guess 'watermarks' can be easily scrambled; add noise, filters, &/or recompress into another image format (eg JPEG -> AVIF).