I probably shoot similar to you, landscape / travel, and bought the 70-300L for the reasons of weight, size, zoom range & quality, in that order.
I already have an old Sigma 70-200 2.8, which is ok, but I don't use it that much (my style preference is wide angle) and the weight of a 2.8 lens is considerable. It was mainly used for motorsport pics.
I did think about the 100-400 but again prefer the wider end of the range, smaller size, better IS & more modern design.
With my 5d3 or 7d, I can crop in quite a bit with the excellent IQ of the 70-300L to get the 'pic'!
I can't praise this lenses quality high enough, and you will see other posts saying the same...