Not true. Banksy sold a painting for $1.4 million and it shredded itself right after the auction ended. Three years later the shredded remains (presumably with the certificate of authenticity) sold for $25.4 million[1]. So, no, the value is not in an intact painting.
Forgers can artificially age paintings. It's amazing the lengths they go to. Maybe something like Starry Night has been analyzed enough that it could be verified, but other works are not. It's not really known how many works of art on the market are forgeries.
> No one would want to buy the certificate from you but let you keep the painting in your vaults
Actually people do this all the time. They pay millions upon millions of dollars for a work of art and it gets loaned to a museum and possibly sent all over the world. They still own it though. There's also freeports[2] around the world with warehouses full of art. You can buy an artwork and it never moves from the warehouse, just the record of who owns it changes.
[1] https://nypost.com/2021/10/14/shredded-banksy-artwork-could-...
The value of art is art. If we disagree then you are admitting that both the art world and crypto are heavily used for money laundering.