Reproduction steps:

1. Open the attached “ModelImporterIssue” project
2. Open the “Assets/Scenes/SampleScene.unity” Scene
3. Open the Build Settings Window (File > Build Settings)
4. Build the Player by pressing the “Build” button
5. Observe the built Player’s size in Finder
6. In the Project Window, select all models under the “Assets/Resources” folder
7. In the Inspector Window, select the “Rig” tab
8. Change the “Animation Type” property to “Legacy” and apply the changes
9. Repeat the 3-5 steps

Expectation: Generic build is smaller than Legacy build
Actual: Legacy build is smaller than Generic build

Reproducible with: 2021.3.38f1, 2022.3.26f1, 2023.2.20f1, 6000.0.0f1

Reproducible on: MacOS Sonoma 14.4.1 (Intel), (M1 (user’s))
Not reproducible on: No other environment tested

Notes:
- The issue is reproducible when building for the Standalone and Android platforms
- The size difference depends on the platform: Android - ~15MB, Standalone - ~3 times smaller