Miner in the blockchain is one who participates in creating transactions of cryptocurrency and also one who is creating new cryptocurrencies and validating their transactions on blockchain. Blockchain is the way of saving data in the form of blocks over blocks and forming all of them in the form of a chain.
Your statement is not true, I've highlighted the wrong one, Minner has nothing to do with the new cryptocurrencies/tokens on the blockchain that are deployed under the smart contracts, by developers. For the rest, it's simple and easy to understand. Elaborating more on this, dinner has the role of validating the transactions made by users, securing the blockchain, and creating new blocks on the chain. The total network decentralization is based on the number of nodes and security is based on the number node participants / minners.
Blockchain is basically a decentralized system that cannot be hacked. Data on the blockchain is present in encrypted form. To hack any particular transaction, the hacker needs to decrypt all the blocks of the blockchain to decrypt that particular transaction he wants to hack.
Blockchain is designed to be a decentralized way to store data but the decentralization of the blockchain may vary from network to network, on the basis of nodes participating in a network as Bitcoin's network is the most decentralized network compared to any of the other Blockchain networks.
Blockchain is secure but there are many things to keep in mind, blockchain attacks are also possible, direct & indirect attacks can be categorized here, the direct attack will be the one in which the hacker attempts a try to hack the blockchain data directly such as by lucnhing 51% power attack. An indirect attack can try to find the variabilities of the Dapps of the network to gain access to the keys and manipulate the assets before getting interacting with the blockchain (Supply chain attacks and smart Contract attacks).