I don’t think either of us are arguing against the Federation reusing old components.
The only point of contention is that you were sceptical that the Voyager A could be a refit of an Intrepid-class starship due to the size disparity, and my argument is that, even though I am personally not a fan, the was the current crop of Trek showrunners have decided to use the term size doesn’t really matter with regards to what is or is not a refit.