I would agree with your T on this issue. I've sat on search committees and I can tell you that, when we are hiring, it is considered a "negative" if a candidate went to the same University for their undergraduate and graduate education. They don't have the same breadth of knowledge as someone who went to two different Universities because they are not exposed to as many faculty, as many areas of expertise, as many disciplinary debates, etc. It also tends to signal that the candidate is "comfortable" at that U and did not have the drive or courage to really forge out on their own and find the best opportunities possible. This is even true of those who went to the same Ivy league school for both degrees.

When I was applying to graduate school, I got the same advice from my advisor. I wanted to go to the same University for my PhD, and my advisor strongly recommended against it. Now that I've finished my degree and am involved in hiring new faculty, I understand just how right she was!

I don't think this is an issue of "therapist" advice, though. I would take the advice because it is correct-- not because it comes from your therapist. I operate the same way when I am given advice by own therapist. I don't take it because she is my therapist. I evaluate it, just as I would if it came from my friend, my dad, my colleague, etc. If the advice makes sense and i agree with it, then I take it. If not, then I don't.