Actually, on my course there is huge emphasis on attachment theory and its impact on the client. It's hardly sweeping over the concepts, we have undergone in-depth experiential workshops examining our own attachment styles and their impact on our work as well as a focus on attachment and MI.
I agree that relying on personal experience alone is dangerous, but personal experience to inform empathy is useful to say the least. My T suggested my past will be 'simultaneously one of my greatest strengths and most significant vulnerabilities' as a practitioner, and I agree completely, so it is my duty to keep that in my awareness.
In my experience of working with therapists, I have found more experienced Ts more beneficial, however it stands to reason that that's not a universal truth, and the individual is a crucial factor in what makes a competent therapist.