after searching out some more around the net, my conclusion its depend on scale and how the app will be distributed.
if the app is small to medium sized and web only, the solution that Calviղ
gave make much more sense. we have more control over the bundle from middleware.
we also dont need to move the bundle from our frontend project to backend project manually, or adding extra buildstep just to move them.
no extra process running that only to serving some static files.
on the bigger scale multiplatform app where our api bandwidth is much more precious, removing extra burden from our backend is the priority, one way is by removing front end serving and put it somewhere else. thats sounds like logical thing to do in that situation.
though its just my personal conclusion, real things may be differ