Transactions still have to be approved by the network. ATM it's pretty slow. And many coins have one pool with majority of the hash rate --> not so decentralized
For most cases you don't have to wait for a confirmation. Accepting a typical non-RBF 0-conf transaction is safer than accepting a credit card payment, because it is trivial to reverse a CC charge, but difficult to suppress a 0-conf transaction sitting in the mempool of thousands of Bitcoin nodes.
«many coins have one pool with majority»
It is not the case for most popular coins: BTC, ETH, BCH, LTC...
