A 25% recidivism rate is pretty good considering that many might have gone to the "battlefield" as payback for their improper imprisonment. Also, it is disingenuous to conflate terrorism with insurgency as both have different motivations and "scope of battlefield."

So-called insurgents were only a threat to local presence of Americans and not interested in sticking overseas or be a part of a broader movement against America. Just because they are fighting for their country from their perspective doesn't make it right to say they are the same as terrorists.

You also have to take into account for the loss of goodwill and reputation across the world for hosting Gitmo; particularly when it has possibly radicalized more people simply by having something to point to when a terrorist recruiter propagandizes about the 'evilness of the US' and the merits of attacking us.

Just to compare, a quick google search shows that the U.S. recidivism was around 70%. It might have improved or not since the study period, but it does perspective on the issue.

Source: http://bjs.gov/content/reentry/recidivism.cfm