I was just following a thought from the OP's theory. Although it makes some sense as follows:
Regulatory Capture involves not just occupational licensing, but artificial monopolies over products and services. For a current example, Facebook has been lobbying congress and even publicly stating that they want to work with them to regulate social media platforms and news media; and even though many can see some benefit to these regulatory laws, the trouble here is that critics argue these types of regulations tend to entrench large corporations who have the legal staff and dev bankrolls to deal with these rules. Actually, many industries, even historically cottage industries such as agriculture has been in modern time criticized in this way as having rules and subsidies written by large industrial, corporate entities which benefit large providers by creating barriers to entry for small competitors.
In short, they create legal barriers to entry to creating the next providers, such as the next Facebook. In accordance with OP's theory, as the opportunities diminish, the value of labor decreases.
But yes, traditionally occupational licensing increases cost and barriers to entry to providing a product or service and is modeled as to increase salaties and decrease jobs as labor supply is constrained.
This is an interesting comparison of orthodox economics as you have mentioned with a reasonable yet heterodox theory in the wild I've seen. I haven't seen OP's theory stated explicitly before. Have you? Unfortunately in economics, we are dealing with the science of studying human decisions and as such it is grossly impractical to create a true scientific experiment here to determine which theory makes better predictions. This is probably also partly why economics tends to be snobby, pretentious and inflammatory: it is ultimately a war of words and mathematical arguments when it comes down to it.