Jonathan,
With one caveat, I think that you have most of the information you need to make a decision. Nobody has talked about the other cameras that you mentioned. I suggest that you do some research on them elsewhere than on this forum.
As the owner of both a BMPCC 4K and an iPhone, I think that both can get the job done. The choice comes down to your personal finances, how you want to interact with a video camera, and future plans. If you’re inclined toward the BMPCC 4K, it is very important that you cost out
everything that you’ll need before you make a final decision to purchase one. Some people buy that camera, attracted by the price, and don’t realise, until after the purchase, what they’re in for financially. That isn’t a reason not to buy one. It’s a reason to go in with your eyes open financially.
Howard Roll posted a photo of his Blackmagic Micro Studio G2 with a Meike lens. As I understand it, it’s the same sensor as the one in the BMPCC 4K. It does not come with a monitor. However, given your
immediate use case, it may be worth investigating.
Re Apple: As you may know, Apple has a 14 day, no questions asked, return policy. Gives you two weeks to decide whether the phone will meet your expectations. I don’t know if Apple is currently selling refurbished iPhone 15 Pros. If you have a problem with an Apple phone that’s under warranty/Apple Care, Apple will deal with the problem very quickly.
Re Blackmagic: If you purchase a Blackmagic camera, I suggest that you buy from a retailer that offers generous returns. B&H does even on second-hand purchases, if you choose to go that route.
If you haven’t already, I’d like to suggest that you look at some videos that have been shot with an iPhone 15 Pro/Pro Max and make your own assessment. Apple shot its last three events, including its June WWDC, on the phone. There are also two short fictional films on YouTube:
Little Garlic , made in conjunction with Chinese New Year, and the Japanese manga
Midnight. Both have English subtitles. Realise that
Little Garlic and
Midnight were made by highly skilled professionals. In the current YouTube style, there are a number of popular videos, such as Joey Helms’s short portrait of Chicago.
This is
Little Garlic:
Midnight:
Joey Helms’s video. As a YouTuber, Helms is a little unusual. He works for Google advising YouTube advertisers. His video on how he edited this is worth watching: