In practice actually iPhone 'fragmentation' is surprisingly bad in terms of how UIs would render unexpectedly on different phones - still probably easier than Android but levels the playing field a bit more, Android market share grew and went more upmarket, cross platform frameworks improved and the whole practice has become less common.
Another way to think about it is that people spend thousands on a new iPhone, they are more likely to spend on apps. There's plenty of data to help confirm that idea such as revenue from apps in each store and even income levels.
From a personal perspective whenever I survey users about what platform they prefer to have a mobile app for with my side projects, it's like 80/20 iOS/Android. When asked if they are willing to pay, it's even more telling that Android users are more likely to not want to pay.
Speaking as someone who built a cross platform framework for a living and survived a major acquisition of that tech to a big tech company and worked in the ecosystem for many years, I believe that although Android may have more devices made and distributed in the world than iOS, it's a much harder market to make money in as a developer. As an existing business, you have to be in the market however.
Nowadays you need apps on both stores, but if you do choose one, do iOS first unless you have a background for Android. There's many cross platform frameworks that can help you do both with one codebase, but if you go native, start iOS in my opinion if you need to make money to survive.
Worldwide, Android phone significantly outnumber iPhones, but in Canada and the US, the split is pretty close to 50/50. At that point we would probably go with the platform the majority of the team is more comfortable with unless there was a specific business reason for going with a specific platform first.
https://billylo.medium.com/ep-19-is-android-app-dev-easier-o...
but.... it's also a catch....you spend more money to develop for apple, so you need money.....hence....you bleed your customers who will 'pay more'....
trusth is.... just as many failures....