Is the indexer centralized? Only in the sense that every server on earth needs to be run by someone, not the sense that everyone needs to use someone else's indexer. You could also run your own indexer, for your own app, etc. The identity network (Mainline DHT) is the most decentralized on Earth. The data model offers seamless portability. The aggregation model is modular. You do not have a technical argument against this system because it was designed intentionally, not incidentally.