Calling it irrelevant is a bit like calling vim irrelevant. Classic calculators don't use REPL, they are designed to minimize the number of keypresses required to input your problem and explore it in the intuitive manner. They use highly efficient modal input languages (kind of like vim). Besides being efficient, these languages tend to have one-off commands you have to remember. Having a cheatsheet on your screen by default is useful for discoverability. In the algebraic calculator paradigm and their typical use cases (napkin math), having a history is not very useful (unlike in RPN where having the stack on the screen is nice).
That said, Qalculate is weird in that it uses a REPL and the input line, which is much slower and clunkier than the algebraic input, but still tries to mimic a classic calculator. It's also slow to start. Not sure what's its use case, as it offers neither speed of a classic calculator nor the feature set of full-fledged math software.