a-Shell should be faster than iSH for local stuff since the tools are compiled natively, but nothing on iOS, as far as I know, compares to Termux on Android.
Edit: well, it's also very slow unfortunately. I believe iPhone CPUs either don't support virtualisation or they don't expose it (edit #2: it's the latter). Either way, QEMU is struggling quite a bit, and due to it being a GUI it's even slower than what iSH could do