The expertise offered here is "how to build a website". If the client is insisting that the dev use a specific javascript library, that would be odd.
The client here is just requesting specific content on their website, similar to someone requesting a granite countertop in their kitchen; that seems fine, even if its not particularly classy or aesthetically pleasing to the contractor.
Do we know that for a fact? You described them as a "web development consultant", but I couldn't tell for certain what their exact role on this project was. Their services page (https://www.nicchan.me/services/) lists both "Web Application front-ends" and "translate your designs into a scalable system", so I think they offer a range.
Both of those sound like expertise in building a website, and not like expertise in business strategy.
To be clear, I would personally have a similar view to the author here. I'm just surprised that they think their opinion on the strategy side matters so much to their client!
It's more similar to someone asking for a cardboard countertop - any contractor would be well within their rights to tell them it's a bad idea and would be negligent if they didn't.
The client here is just requesting specific content on their website, similar to someone requesting a granite countertop in their kitchen; that seems fine, even if its not particularly classy or aesthetically pleasing to the contractor.