Smooth but for many years, smooth only until you tried to switch app. iPhones did not have enough RAM to really do more than one thing at once, so multi-tasking came years late and the legacy of that is still present in the very weak, hacked together way in which apps collaborate on that platform. Perhaps this lack of emphasis on multi-tasking and linking apps together is partly due to the decision to AOT compile everything, creating additional RAM pressure. Also, Android was able to scale down to cheap devices, and scale up to very high end devices. Apple basically ceded the entire budget smartphone space to Android, they didn't even try, and budget phones (especially in developing countries) are often characterised by being RAM constrained.
Interesting. I was under the impression that Android had more problems with RAM pressure than iOS, because Android uses tracing GC rather than reference counting. I observed that as late as the iPhone 6, the flagship iOS device had only 1 GB of RAM, whereas contemporaneous flagship Android devices had 2 or 3 GB. I guess I succumbed to the tendency to assume that Apple can do no wrong, leading to the assumption that Apple shipped with less RAM because they didn't need it, not because they were just being cheap.
GC technically speaking can reduce the amount of RAM you need, as it can compact the heap whereas a native malloc can't. In practice this effect is hard to measure as the sorts of languages that use compacting GCs tend to be rather pointer and allocation happy, so any gain from compaction gets outweighed by other factors.
The specs of the various devices have changed over time. Android scales better: you can give it very little RAM, or a lot, and it'll make best use of it by e.g. keeping more background apps loaded at once. iOS was at least historically much less flexible about this: boosting RAM was not worth as much as in the Android space because app devs would still target older devices for quite a while and so the additional RAM would go unused, and the OS wasn't capable of using the spare for much due to the lack of multi-tasking.
Eventually Apple implemented Android-style task switching, so I don't know if that's still true. I haven't done any mobile dev for years. But I also think at some point Apple realised nobody who buys an iPhone actually cares about whether they're getting value for money or what the specs are, so they just stopped competing on that area. I mean they have never reduced the price of the iPhone once, right? Despite the huge fall in underlying component prices over the years. They could ship a device with 128mb of RAM and if it did the same thing as the iPhone 4 people would still buy it, simply because they see themselves as iPhone users and not "smartphone users.
It goes to show that several factors influence the performance, memory usage, and real hardware requirements of a platform. I'll gladly admit that my original, simplistic assumptions were wrong.
ObjC, as typically written (i.e. more object-oriented than C), is also pointer and allocation heavy. so that might make compaction more of a benefit for Android. I wonder what proportion of memory in a typical Android application process is on the C heap rather than the garbage-collected, compacted heap. For example, where does image data usually end up?
To throw in another complication, are there any significant problems that come with layering a garbage-collected runtime on top of a high-level framework based on C heap allocation and reference counting? That's what Xamarin, React Native, and AOT Java runtimes (e.g. Multi OS Engine) do on iOS, and what .NET (even .NET Native) does on UWP. Or how about two garbage-collected runtimes in one process, e.g. Xamarin and React Native on Android?
Google did lots of work to fit Android on 512MB devices, also modern Android does use a parallel concurrent GC with just one pause. They also made the JNI stricter, in order to allow compactation on future versions.
Windows Phone .NET runtime also uses tracing GC, although the underlying UWP APIs are COM based.
So it's a complex topic.