But in NFTs the picture is not on the Blockchain. Only a link to the picture is on the Blockchain and the picture itself is still just on the web.

It works more like loaning money and then receiving interest, except you are loaning crypto to the network and then you get it back, plus some, after a certain period of time

This would just create a fork in the blockchain where 51% of the network doesn't match the correct state of the blockchain that the 49% have. The 49% would effectively stop working because they could never validate the transactions that the 51% takeover has falsely created. The node operators of the 49% of the network would need to reach consensus for how to deal with the problem, but essentially they would just adopt code that ignores the 51% data, so they could continue to process blocks of transactions. Without manual intervention the 49% would be frozen. The 51% is just fake, they haven't really changed anything because every real node operator would know it's false data.

Is it easier to establish a source of trust? With blockchain trust lies in the protocol and in the node operators who make decisions about how to operate their nodes. Running a node isn't extremely difficult. Running a financial institution is difficult.

That's really rude