SWF
is a compact format, but that doesn't get you an efficient Flash Player. Apple put in a
lot of work to make HTML battery efficient and usable on a phone, and Adobe didn't[0] do the same with Flash. In fact, Apple more or less begged Adobe like four times to make Flash work well on phones! Adobe wanted to push that work onto their customers instead of putting work into making
every Flash movie ever authored work good on a phone.
The real bullshit about the Jobs Flash memo wasn't that it was justifying not shipping Flash Player on phones, but that it was justifying banning apps that used any third-party developer tool. Adobe had decided to just ship a packaging tool that let you stick a SWF and Flash Player into an iOS app; which Jobs considered to be a way to pollute the App Store with garbage apps. Except this wasn't a ban of one specific developer tool, it applied to everything that wasn't entirely C, C++, Objective-C, or JavaScript[1]. This only lasted about 3 months because...
1. A lot of mobile game developers were already using scripting tools that violated the new rule, and the games they were shipping were not garbage
2. The FTC was threatening to sue Apple
After that, Apple caved completely. In fact, if you've played iPhone games, you've probably already used Flash Player on iPhone. Jobs' fear was mostly unfounded because developers absolutely could make performant mobile games in Flash and ship them as apps. The problem was that they had to work around all of Flash's legacy crap to get there.
[0] Safari has several UI affordances for mobile web usage that Flash never got. Notably, those "cutting edge floating menus" still work because Safari treats finger touches as either a hover or a click, and picks between the two based on how the page changes when it simulates a hover.
Furthermore, browsers around this time were moving to GPU compositing internally, but Flash has always been built around a particularly quirky scanline renderer. Getting that to work on GPUs was apparently too much for Adobe, and even Ruffle has rendering problems caused by it.
[1] The language in the developer agreement was "originally written", so no, transpiling doesn't get you out of this.