As with everything in engineering the definitive answer is "it depends".
If your JSON API is guided by your UI then you are gonna have a fun time keeping with the changes (been there, done that). Sure you know that to add a new field on your page you will need to add it on the API's JSON, then on the JS client code, then on your client template... Compare this to adding it on the HTML generated on the server and... done!
You need to implement a deadman switch. For example if using Prometheus you can configure it to access an HTTP endpoint of a deadman switch service every X seconds. When that service detects you have not accessed it in some time it will alert you.
If your JSON API is guided by your UI then you are gonna have a fun time keeping with the changes (been there, done that). Sure you know that to add a new field on your page you will need to add it on the API's JSON, then on the JS client code, then on your client template... Compare this to adding it on the HTML generated on the server and... done!
There is value in differentiating between Data API and Hypermedia (UI) API, you can read more about it here https://htmx.org/essays/hypermedia-apis-vs-data-apis/
And note that is not an universal truth applicable on all cases because "it depends"