When I rebuilt my Bianchi, I intentionally installed triple shifters but a compact double crankset. I can switch to a triple if needed without having to change anything else. The front derailleur is a triple as well, and the bottom bracket is external (Hollowtech II).

As long as my limiting screws are set properly and the cable tension is adjusted, I don't have any "extra" or "dead" clicks in the front shifter. Even with a triple FD, I do have to trim in the small ring, but it's ok now that I've learned when I need to do it.

Without seeing the bike, I'm inclined to agree with your mechanic that it's cable stretch. I might start from scratch with the front derailleur and unbolt the cable entirely, then re-install it to ensure that I'd gotten all of the slack out and didn't have any "dead spots" in the front shifting.