Modified Tukey window applied in frequency domain
Regarding the 2:1 frequency ratio recommendation for the transition band (f2:f1 or f4:f3):

The steeper the filter response (i.e. the smaller the frequency ratio between pass band and stop band limits), will necessarily produce a much longer impulse response and produce ringing artifacts in the time domain whenever there is a transient.

These filters, which are applied in the frequency domain, also seem to have linear phase response, which is very desirable for analysing this type of signal.

Butterworth filters have a compact and nice representation as difference equations (for filtering in the time domain), but do not have linear phase response, and as you see from your plots, have not very good transition between pass band and stop band.

(I don't understand how you plotted a symmetric impulse response (time domain) for Butterworth filters; their impulse response is causal and asymmetric in general.)