Is decentralization a selling point?

For me, decentralization isn't valuable in and of itself.

The decentralization needs to exist for a really good reason, since it certainly increases complexity. In the case of blockchain specifically, it also usually comes with performance costs, difficulty of cost estimation (I now have to estimate what my transaction fees will be rather than having a known or easily calculable recurring cost), and environmental impact (due to power usage).

So the question I ask myself when considering whether or not something should be decentralized is:

Is the value I'm getting from decentralization outweighing the (I believe significant) costs?

In your case, you seem to highlight two main sources of value: lack of central authority, and scalability.

I'd say the lack of a central authority is appealing to me only if I'm making something that I would reasonably expect to be at risk of censorship in certain environments, such as an app for political activists to organize on. There probably aren't too many apps in that category, but for the ones that are, I can see it as being extremely valuable.

The scalability element I'm not so sold on, since blockchains famously have scaling and performance issues and there are lots of great scaling solutions out there already that have known costs tradeoffs (for example, we're currently using Cloudflare Workers and a serverless architecture at Consentry and it's been a wonderful experience so far). Maybe for the specific use case and the sort of scalability you have in mind, blockchain will provide unique benefits, I'd be interested in hearing more details if that's the case.

Check out https://www.stateofthedapps.com/ if you haven't already. Some of the adoption figures are very poor.