Piers gets a lot of slack but he's more than qualified and a very good interviewer. I still think 'You Can't Fire Me, I'm Famous!' and The Dark Side of Fame which he did for the BBC were superior to Life Stories.
I'll admit he's good at his long-form interviews and gets a lot out of his guests on such programmes. But much of his interviewing on GMB seems to involve shouting at, and over his interviewee and obsessing over one point which very often is a side-issue to the matter in hand, like some kind of Poundland Paxman.
I often feel the purpose of his interviews isn't to find out anything new, but just to make him look clever and the interviewee look stupid, whilst Susanna sits there mute, rolling her eyes.
I may be on my own here, but I don't believe aggressive interviewing is good interviewing.