I'll note that one of the reasons that path is different from the other, is that you asked for directions from "Harvard Square" or maybe "Harvard Square Station", right?
If you're actually coming in on a northbound train, it saves you about a block's worth of walking to use the exit that the bad Google Maps public transit directions use, instead of walking back down the platform, and down the ramp, and then up to the surface in Harvard Square proper, as per that.
@unlambda
I'd argue that the correct directions, if you're coming from a northbound red line train, are to use the north head house to exit on the east side of Mass Ave, next to Harvard Yard, and just stay on the damn sidewalk. You have to trust the process, but it will deliver you unimpeded directly to the Science Center plaza.
And it has the advantage of being a path that works even with Harvard has locked the gates to Harvard Yard (e.g. around graduation time.)
@whitequark