With the GN args:

is_java_debug = false
multidex_in_release = true

Building monochrome_public_bundle, we have the exact same .dex files as with:

is_java_debug = false

Which is:
   473052  2018-10-29 16:08   base/dex/classes2.dex
  7034200  2018-10-29 16:08   base/dex/classes.dex
    20692  2018-10-29 16:08   ar/dex/classes.dex

The main classes.dex is full (65498 methods), and the secondary dex is just overflow.

Ideally, we would have the minimal main dex when multidexing, which would make the main dex ~10k methods and the secondary dex take the majority.