While I would certainly would be excited about a Brad Stevens hire, I do also share some your pessimism. As you said, he has not coached college basketball in 15 years. He also didn’t coach college that long. While he did reach national championship games in a row, which is a great accomplishment, he did so in two of the weakest years of college basketball. He also had double-digit loss seasons in 2 of his last 3 seasons out of the 6 total seasons he coached in college (granted, he reached the national championship in the first of those), with his second to last being 22-15. In the years he did not reach the national championship, he never made it past the first weekend of the NCAAT.
Again, I’d be very excited if he were the hire, but I’m not sure he’s as proven as many people think.