This is clearly flawed.
Whether you like it or not Forest are a bigger club than Palace.
Based on your last 2 points we are bigger than Man Utd, and we are clearly not.
Having a passionate fanbase is irrelevant to a club's size. Selhurst has a 25k capacity, Forest is almost 31k, and sells out every game. Not only that with our limited hospitality our revenue on match days is limited. Forest's match day revenue will far exceed ours (just like new grounds such as Spurs and Arsenal get more matchday revenue than Man U despite having smaller capacities).
However, i think it is fair to say Forest isn't a massive jump up on Palace, making Glasner's decision a little strange. However, i suspect no big 6 club will touch him and Forest has made him an offer he couldn't refuse.