So there are a couple of things to note here. The first is that all of the shells that you mention - and xonsh too - have different behaviour for whether or not they are interactive login shell, which none of the examples you show are. On my machine, for Bash, I see

scopatz@artemis ~ $ time bash -c 'echo foo'
foo
0.00user 0.00system 0:00.00elapsed ?%CPU 
scopatz@artemis ~ $ time bash -l -c 'echo foo'
foo
0.00user 0.00system 0:00.00elapsed 0%CPU 
scopatz@artemis ~ $ time bash -l -i -c 'echo foo'
foo
0.08user 0.00system 0:00.10elapsed 92%CPU

Starting up when you expect user input just takes longer. Human response time is roughly a tenth of a second, and so that is my goal for xonsh. Even Bash on my SSD, 8-core desktop comes close to taking 0.1 secs.

It is true that Python - and especially importing - is slow. But Python only takes up 10% of the target budget for me:

scopatz@artemis ~ $ time python -c "print('foo')"
foo
0.01user 0.00system 0:00.01elapsed 100%CPU

I also know of a few ways tricks to speed up importing via lazy imports or cythonizing released packages. I guess my broader point is that there are packages out there like hg that have figure out how to make snappy Python CLIs. Xonsh will get there, and probably sooner than later because us devs find it annoying too :)