But otherwise there's no advantage compared to a traditional database that I can see...
This is similar to how I was always worried that Bank of America would arbitrarily change the balance in my account for some reason, but bitcoin solves this problem. Now I just have to worry about losing my password or getting hacked and losing all of my money, and that's just much less realistic than a major bank abusing their centralized admin powers to change my balance.
If Bank of America deducts money from your account, you can call customer support and threaten to file a complaint with a regulatory agency, threaten to close your account, or just take them to court. No guarantees that you'll get your money back, but at least there's a chance.
If you lose your wallet password. It's game over. 0% chance of ever recovering any of that money.
How do you prove that said NFT is issued by OEM?
How do you avoid NFTs being issued by the seller themselves?
That's still rather convoluted.
The same thing applies to other similar "NFT as certificate of authenticity" schemes I've seen, such as around luxury goods.
That sounds like a convoluted and impractical solution looking for a problem. Mobile service companies and hardware vendors managed to implement services that support activation and bricking without getting any crypto-related buzzword in the way.