Agreed, he should have been correctly penalized at the time. Multiple 5s penalties may have changed his finishing position and given other teams points, which is huge for the lower teams.Grid penalties before a race are the most useless punishments in F1 unless we're talking 10 places.
Whether a top car/driver starts in 1st or 10th it really doesn't effect the outcome over 60 laps.
They need to find other forms of punishment.