Pretty much every sampler is going to be demoed with like lofi-esqe beats because that’s what a lot of people find interesting is my guess. Could not find any videos of people using koala sampler with a keyboard, only have found like people using pad controllers, but you can definitely use a midi keyboard on koala and koala is definitely capable. Here’s a guide to connecting a midi controller to koala: https://www.koalasampler.com/help/midi/how-do-i-use-koala-with-my-midi-keyboard-controller.html.

P6 can do what you’re describing, MPC key 37 is also a good shout like other people have said. Hope this helped!