Native Sliding Sync (AKA Simplified Sliding Sync) was just released to Synapse and Element X over the past couple of weeks. It’s not an exaggeration to say that it is FAST now. My fairly large account usually syncs instantly now. If not instant, the longest I’ve seen was 1 second. Give Element X a try again (assuming your home server supports SSS).
Android and iOS EX actually both use the rust SDK under the hood, but iOS is usually used as the test bed so it gets features a little faster than Android. EX iOS just got a stable version of it a couple days ago, so a more native feeling login process for SSS on Android should be coming very soon!