The business cost with PRs isn't the first review but another developer, it's the number of iterations on a pull request due to defects and change requests. The way I am trying to promote the use of LLMs with more junior developers in my team (I am the CTO) is to use AI-assisted tools (we used Windsurf and recently switched to Github Copilot) for a first pass, e.g asking the agent for a review and catching potential defect before involving the human reviewer.
This doesn't mean the human reviewer will need to spend less time reviewing, but potentially this PR will be merged faster with on average a lower number of iterations and improved code quality.
I do have in my team some senior developers that are excellent, and it's very very rare I catch an issue in their PRs (maybe 1 out of 50). But I also have greener developers for who the ratio is way higher (like 8 or 9 out of 10) and this means repeated context switching for the reviewers.