TOS are contracts
By agreeing to the terms of service you are entering into a legally enforceable contract, just as binding as a contract for buying a car, taking out a mortgage, or buying a cup of coffee. The common law makes no distinction between contracts just because of their size.
Also, the law is that if you enter a contract, you know what you are doing. It is not the law’s job to help you just because you knowingly made a bad bargain.
Now, these contracts can be void or have unenforceable clauses for the same reasons that any other contract can. For example, the common law has long refused to enforce unconscionable terms. More recently, many jurisdictions have passed consumer protection laws which may further limit what is and what is not legal in a contract.
Refunds
You are only entitled to a refund if there has been total failure of consideration. That is, if the other party has done nothing they promised to do.
So, for example, if you paid for a skin and technical issues meant that you could never access it, you would be entitled to a refund. However, if you could have used it at all, even briefly, you have no legal claim for a refund.
Now, in the modern world, many businesses will offer refunds as a goodwill gesture or a business strategy even when these are not legally required. But that’s a business decision, not a legal one.
Ownership
Go and read the TOS, I’m really sure that they don’t give you ownership of anything - they give you a licence to use the virtual goods and services, not an ownership right. This is fundamentally different from your gold broker example where you do actually own the physical gold.
While not completely accurate, a licence is more like a rental agreement than a purchase agreement. Think Avis rather than Ford.
So, you don’t own your account, avatar, skins, etc., you have licence to use them aSas permitted by the TOS. If the TOS allow the supplier to revoke your Licence, then, providing they filledfollowed the TOS, you can’t use them anymore.