The answer is that it often is not, at least for most people, most of the time. Eventually it will be the best payment system, but it needs to develop further, gain more adoption, and get over the scaling obstacles. Even so, Bitcoin is already the best payment system for certain use-cases, such as sending money across borders, or receiving money from someone you don't trust (which helps further in cross-border transactions).
I agree. As of now, Bitcoin as a payment system is only good for certain transactions but definitely not all. Bitcoin is perfect for transactions involving large sums. But for little payments such as a meal or a pair of shoes or a piece of T-shirt, Bitcoin may not be perfect as the fee is a little higher. Indeed, international transactions are also perfect for Bitcoin as it is borderless.