Discussed at length when the new Codex came in. Here's a link to a previous thread
The argument of "replace all weapons" meaning "replace all stock weapons" is bokum, your friend is adding wording that simply isn't there - "all weapons" means all
The only way you might get away with it is the "take the TH/SS first, then upgrade with CML because even though the list says 'replace storm bolter' is also says 'doesn't replace storm bolter' later on..."
, but even then expect arguments every other game.
I'm of the opinion that it isn't an option anymore, despite GW
flip-flopping on the issue with FAQ
's throughout the lift of the 6th edition DA
codex. Which is a pain for those that had modelled one (but I'm happy being able to take TH