Nostr fits into the picture by not promoting algorithmic feeds and only showing what your followers post, thereby removing the toxic sludge of attention-grabbing content solely for the purpose of data harvesting, which is used to fund operations by sending it to third parties. We can simply opt out by choosing #nostr
Who's to say that #Rumble won't operate the same way Big Tech currently functions? Is it decentralized? No. Is it open source? As far as I know, only its content moderation tools are open source, but that's about it (feel free to correct me if I'm wrong). Is it censorship-resistant? They claim to be, as designed. However, since they have a CEO and board of directors, they have to answer to somebody. So, it's only a matter of time before it won't be as censorship-resistant as they claim, especially under governmental pressure.
So, where does Nostr fit into this? It fits by serving as a decentralized, open-sourced, and censorship-resistant protocol that doesn't serve any single entity, unlike a centralized platform like Rumble