@Palanthraxgood point. but please keep in mind. it's not (only) about the apps the user starts manually. It's all about the wonderful dandy helpful background tasks. That make things smoother in your live. That poll data. Pretty much everything has a task by now, has a service, runns in background. And it is possible that in the new operating system (I assume that on iphone 11 it's a newer iOS than on iphone 7) that there's more tools, more tasks running nin background. by it by operating system, be it by the apps that recognize the newer environment and make use of different techniques.
That's like the real "random" value. I notice that myself on the android. I clean up all "running" apps, wait a while and there's always a different amount of memory consumed after a while. Without me starting anything. It's background tasks, pollers, services, that are being started / stopped by the operating system / apps / ...
And I assume that swgoh most likely will store every glyph of every thing they show in memory, not using weak references, not cleaning up the memory for "dialogs" once they closed the dialog. Hence holding more and more data in memory, not releasing it.
In my eyes memory still may be a good indicator to look at. As you stated, the hardware itself may be better (like cpu wise). But please keep in mind, there is pretty much NO mobile out that really has more than 4 GB of ram. Rather less (2gb, 1 gb) ... so ram is the biggest limitation.
Between S7 and S9, the ram has not changed. It's still 4 GB ... and at least for my android device it clearly was stated by the operating system that it was an out of memory exception (and prior to that garbage collection which heated up the system and drained battery).
So ... one other hint for you that it may be memory related is that ... if you run into that performance issue/freeze... your battery gets drained (way ) faster than if you didnt start the app, and your mobile got hot.