Simple question. If you do squats and deadlifts and the next day your lower back is sore to a point its not a good sore necessarily, would the best way to build up the strength in that region be the Roman Chair and Back Extension machine?

Roman Chair
https://www.youtube.com/watch?v=ZjCdQtx38Xk

Back Extension Machine
https://www.youtube.com/watch?v=xuJoW96gBbg

These make sense to me but I have seen some accomplished lifters who don't do either of these (but complain of lower back pain)