1. libpython3.so has soname "llibpython3.so" due to needless "l" in "-Wl,-hl$@".
2. libpython3.so is not linked against libpython$(LDVERSION).so when -Wl,--as-needed flag is used. -Wl,--as-needed flag is used by default in Gentoo due to major benefits.
From `info ld`:
`--as-needed'
`--no-as-needed'
     This option affects ELF DT_NEEDED tags for dynamic libraries
     mentioned on the command line after the `--as-needed' option.
     Normally the linker will add a DT_NEEDED tag for each dynamic
     library mentioned on the command line, regardless of whether the
     library is actually needed or not.  `--as-needed' causes a
     DT_NEEDED tag to only be emitted for a library that satisfies an
     undefined symbol reference from a regular object file or, if the
     library is not found in the DT_NEEDED lists of other libraries
     linked up to that point, an undefined symbol reference from
     another dynamic library.  `--no-as-needed' restores the default
     behaviour.

I'm attaching the patch.