Realistically they are not irreplaceable. They provide convenience for coordination of some stuff but a company that would be able to sell smartphones at scale

Realistically they are not irreplaceable. They provide convenience for coordination of some stuff but a company that would be able to sell smartphones at scale with an alternative OS could get there pretty fast. All the very useful apps are some sort of marketplace/coordinating software (with an identity/messaging system) that already has a web version anyway. The major issue is the massive web index since that would take a lot of capital and time to recreate but there are already various alternatives that could get better with use. For the commercial web it doesn't matter as much since it's always evolving anyway and every big website already has its own search engine. Would be inconvenient at first but not something that would affect people's lives as drastically as tech people like to think.