[synthecypher]

First thing that comes to mind is can any of his suggestions be enforced with linting and/or CI jobs?

If so then maybe defer his changes until they are implemented in linter and/or CI job configuration preferably at a company, team or project level.

If this is something more debatable like how a feature was implemented (there are many ways to skin a cat, all of them wrong). Then I would suggest they provide their suggested changes and maybe even some BDD-style tests that would not pass given your implementation.

If they don't have the time and still insist on you doing things 'their' way, maybe inform your product owner or project manager that you are spending extra time working on this feature but it will not result in delivering any additional value to your users/customers and have the reviewer take up the discussion with them.