the in-game assets you purchase are actually yours. This means you can use/sell them outside of the game
There's nothing in "blockchain" or even "Solidity contracts on Ethereum" that make it so this would naturally happen. If the in-game purchases are general transferable tokens, then yes, that could be one possible implementation, but the game needs to support that.
Your dev team's node is the only one that can write the transactions[/quote]That's not how proof of stake / dpos works
You can easily set it up such that you need a particular private key (wallet keys) for initiating certain kinds of transactions in whatever smart contract you use.