transaction times and finality in the blockchain are two different things. Immutable transactions on a blockchain are time based, it's why exchanges need more confirmation times for some coins than others. Fast block times don't mean they are as secure as long block times. A bitcoin transaction with one confirmation is more secure than a litecoin tx with two confirmations.
With segwit transaction malleability will be gone and tx are instant, immutable confirmations will still take time. Lightning network will eliminate the need to wait for confirmations for all but the transactions involving millions of dollars in value.