Is this a proper usage of "that is"?

I've recently heard "that is" being used in a sentence with the following structure:

Beethoven has created the masterpiece that is Symphony No. 5.

This sentence feels a little bit awkward to me. Is it a valid use of "that is"? And Is there a better way to express the same meaning?

I've gone through past questions involving "that is", but this phrase is more commonly short for "that is to say" and convey "in other words". Is it being used in a similar fashion here?

Solution 1:

Use of the definite article “the” indicates one masterpiece rather than one of many that might be indicated by the indefinite article “a”. In this case “... the masterpiece” refers the reader to one masterpiece, but to which?

There are many masterpieces in the world. Even if we understand from context that the reference is restricted to the works of Beethoven, which one?

The reference is completely defined by saying “... the masterpiece that is Symphony No. 5”. I suggest this justifies the construction.

I give you two fabricated examples:

“When we look at Europe and see the disaster that is Britain today, we despair.”

“We admire the expression of Jane Austen’s genius that is Pride and Prejudice.”

In these sentences and in yours we move from an undefined definite (introduced by the) concept drawn from a limited set of possibilities (works of Beethoven, various disasters in Europe, novels by Miss Austen) to its exact definition (which composition, which disaster, which novel?)