As has been said, how does the game engine enforce ownership of those assets? The best it can do is query a blockchain (and for p2p games without central server every client must also become a node in all backing blockchains) and check ownership of corresponding private key[s]. There is absolutely nothing stopping you from minting a new NFT describing in-game assets, therefore the *content* of NFT must be signed by players in a match or some other external entity, but the blockchain makes no guarantees about the content.
Most of the blockchain properties only apply to on-chain assets. The very moment you involve an off-chain party, blockchain becomes append-only database with performance of table top calculator and latency of postal pigeon and is therefore a shitty database.
The only valid use case I see is a smart contract that automatically issues certain assets, which could be seen as somewhat of a solution searching for a problem, but games are not the problem. With games all clients must agree on game state anyway, storing game state on the blockchain is too expensive/cumbersome and if you have to agree on game state anyway, the state can also include assets.