Why Would A Schema Make An Xml Column Slower?

I have a table with an XML column. The documents are pretty large and numerous, and I've been trying various ways to improve the performance of basic queries. Because the document

Solution 1:

I think you've got your answer right there:

I should note that the schema itself is rather large and elaborate

A complicated schema can be computationally intense. If you're doing much in the way of updates especially, the schema has to be validated multiple times.