You do not have to have a breath test to diagnose sibo. Most docs will give you a course of rifaxamin and if you improve, then its probably sibo. But if they think it might be pouchitis, then a scope is probably in order.
And yes, Shen definitely knows what he's talking about. I no longer have a jpouch. But a week after a hospitalization in which I had serious doses of two types of iv antibiotics I started having serious gut problems, extreme belching, distended abdomen, pain, and most importantly significant weight loss, etc...one of the warning signs of extremely serious SIBO. Shen told me it was sibo, simply based my symptoms.
He put me on an antibiotic it sort of worked. Told me to cut out sugar and reduce carbs. It sort of worked. But then things got worse, even more weight loss. Told me to try a FODMAP diet. And within 2 months I was a new person. So it doesn't necessarily take a year to get things reorchestrated in your gut. And definitely diet can make a difference. Many of the things that are ok on paleo are not ok on fodmap elimination. And some of those are defintiely problematic for me. However, I am ok with certain carbs.. rice pasta, rice bread, etc. So to each his own. But the main message here is diet does make a difference.