NFT cannot be exchanged for another NFT as they are unique and valued differently while other currencies are interchangeable or fungible i.e., One Steem equals another Steem and so can be interchanged.

Every NFT is different, there is no similarity between one and the other. So one NFT cannot be exchanged with another NFT. We naturally see that other currencies or cryptocurrencies can be exchanged with one another. Because both are equal. But in the case of NFT, each is unique. So it is not possible to exchange one NFT with another. You have a very nice discussion about NFT. I really like your discussion / you have been able to present very important issues.