Why can't people just play Blockland on its target system?
This. If you want portable blockland, get a laptop.
You need to fit:
WASD, a way to aim, left click, B, 1-9, 0, space, shift, l, right click, scroll, q, esc ad probably some other buttons I'm forgetting. That's 22 buttons + a scroll wheel and a way to aim for a comfortable blockland. If you really needed to, you could remove the 1-9 and 0 to make it 12 buttons, but that's still way too much to fit on tiny iPhone screen.