Based on what objective fact? Is he napping when he should be on duty? Is he taking fewer recruiting trips, head coaches only close? Is he letting staff do more?
I agree he may have been distracted during the final planning and building the stadium, but that's a supposition that's not been confirmed by anyone reputable.
You may be tired of Robe, he may have problems with today's youth but to call him semi-retired is a low blow IMO.