I am not sure where this idea came from, that the python tests are included in the modules. They are all separated in files that are called test_SOMETHING.py.
As of why is this better, there are a number of things that AFAIK Test::Most does not support - for example
- running individual, independent test functions (e.g. subtests) on their own
- having a fixtures that will run before and after each subtest.
Test2::Suite - as far as I understand it is primarily a new harness and it also provides a front-end similar to the one provided by Test::More world (ok, is, like, subtest, etc.) This module is an alternative front-end using Test2 behind the scenes.