When traveling to BC I walk to the BC spur’s stop (Hynes) and that walking time isn’t much from many places on campus. It may still be close to the same as the North End, but that’s still a good deal of time. I know some BC and Tufts students, and they go into the city significantly less because of their location, and often express frustration with it when the are in the city. I do think Tufts is better if you prefer the Cambridge area, but it isn’t quite the urban/city experience if that’s what you’re looking for, at least not as easily accessible.
I’m very familiar with all of the areas you listed and their travel times.
That’s not my idea of close. From any of the colleges I listed, you can get between them easily and to downtown within 30 minutes on a good day. That type of access makes it very easy for students to take advantage of what the city has to offer. BC faces significant commute times and Tufts, while better for Cambridge, faces an added 15 minutes to that 30 minute radius. I’m not saying they aren’t in Boston or don’t have access, I’m just saying that for a college student, via people that go there, there’s a difference that significantly affects lifestyle.