using your example all cryptos are centralised if you use crypto without mining them?
No, the context is networking between blockchains.
If they're networked via a hub, then the network is centralised.
This is true even if the hub is blockchain-based.
In such a scenario (e.g. Atomic, and also sidechains in a different way), a central blockchain records transactions between all other blockchains. Thus, even though the central blockchain is internally decentralised, its position in the inter-chain network is as a centralised entity.
See what I mean?