KSEW can manufacture ships and submarines using kits of materiel (KoM) from the original supplier.
This isn't assembling as there's still manufacturing involved (e.g., cutting steel). However, the KoMs would include all of the critical inputs such as the steel and engines.
Pakistan doesn't produce any of the inputs indigneously. So, with ToT deals or even original designs, all of the engines and steel have to come from abroad. We basically didn't advance much since the 1970s and used 50 odd years for development to ruin our industry.