Please correct me if I'm wrong, but that sounds like a very narrow use case, and also something that could be solved by simply stuffing JSON into a RDBMS.
However, perhaps there are tools that NoSQL provides that are handy.
Then argue honestly and work to steelman other's arguments. To address your point, I'd hardly consider IoT platforms to be a "narrow" usecase. Smaller than the whole of computing, surely, but it's a growing field. The reality is that more and more devices will become available that generate all sorts of hard to predict data. Being able to handle those easily will be a large strength for platforms going forward. Dropping this hard to predict data as JSON into a RDMS will certainly come back to haunt you in 5 years.
You'll have dumped it into a strict database, giving yourself a false sense of order and organization. But later when you need to query that amorphous data, you might be able to use OPENJSON or something else, but a NoSQL solution will have been built to handle this type of query specifically with utilities like key exists and better handling for keys missing or only sometimes being present.
However, perhaps there are tools that NoSQL provides that are handy.