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.
W.R.T. compositing, browsers took a long time to move to even just GPU based compositing, and full GPU based rendering took longer still. Certainly, if Flash hadn't been killed off so prematurely it seems reasonable that either they'd have done the work to keep up, or users would have organically abandoned the platform.
Indeed, you make a good point that it was really a fight over forcing devs to use Objective C and nothing else. Flash was just roadkill in that fight.
The same people will say Flash was slow by default. I remember running canvas vs flash rendering tests in mobile Safari when the plugin was still available, and Flash blew canvas rendering away. Of course it was all about what you chose to do with it... no one was writing really complicated behaviors in canvas at that point, and wasm didn't exist, so if you wanted special animation or complexity you used Flash. The appropriate thing would have been to have Flash off by default until someone tapped an embed to load it.
It took a few years for plain old HTML/JS sites to be optimized for mobile, and not many of them were then. Given some time, Flash devs would have too. I'd already optimized my own and was optimizing a Flash-based gaming site for mobile when Apple pulled the plug.