Yes, secondary, slow, board-level thermal protection is often necessary, the approach is fine.
Just design the semiconductor side (current sensing, limitation, part rating, etc.) so that in no instances heating is so fast the board-level sensor can't react to it. But part ratings need to be based in some ambient temperature and this means local ambient near the board, and board level sensing and protection will limit this Ta to some sensible value like 60-70 degC leaving some 30-50 degC over RthJ-A.