At a basic level, it's not. If i had to teach a total beginner how to play a punk song for a gig tomorrow, i'd teach him the bass part because playing chords does require a certain kind of coordination and musculature. However, once you get past that basic level, i'd say bass is harder. Take any technical run or lick on guitar and transpose it to bass; it'll be 10x harder to execute because of the wider spacing and also because we have fewer strings, so you have to shift positions a lot more than on guitar. Now, i will concede that the straight fourths tuning does give you less to think about when your playing technical parts, but this can be negated if you tune the guitar in fourths.