Here's Emerge Tools' size analysis of United's Android app: https://www.emergetools.com/app/example/united-android

As you can see from the breakdown: 34% of the app is native libraries, another 34% is dex, 23% is resources, and another 8% is assets.

Unfortunately they're still not using AABs, have about 4 MB of download size savings from just image optimization, have 1.1 MB of Emoji gif files , and are not optimizing their Native libraries for the specific architecture (using AABs would solve this)