The real challenging part is to make a self-sustaining tokenomics for the game. With the help of good tokenomics, people can make some earnings from the game, and at the same time, people are also able to invest in the game.
I think this is the key point a lot of people miss too often when it comes to P2E/blockchain games. The idea isn't that the game directly rewards you through gameplay (though, in cases of tournaments this can work) but rather that players have the ability to create value through their actions and trade with other players. A true hypothetical crypto MMORPG may see some players as blacksmiths minting swords and armor as NFTs, who have to buy ore tokens from players who decide to specialize in mining.
Unfortunately this boils down to time arbitrage at the most basic level. If the gameplay loop isn't engaging enough for all playstyles, the most profitable strategy will become the meta and the economy can break down.
Thankfully we're seeing more games adopting better gameplay loops now that can be more fun and serve as a game first instead of a gamified crypto faucet.