Average AHL arena capacity is 9,816. This alone would cause relegation/promotion to be a non-starter.
The goalie argument about talent dilution is valid and NHL teams are due for a rethink in how they approach this position. Skaters, coaches, management etc., there are plenty and this is not a real concern.
I suspect people are not considering with each introduction into new markets, young fans are born, youth programs are created and local development occurs. Young athletes who would not have been exposed to hockey, see games, become fans and go on to become 60+ goal scorers in the NHL. Sure, you need more players but, the pool to choose from increases.