I'll give you top half, but I wouldn't list JimBo as a top-10 GM.
I'd put him between 11 and 15 with guys like Steve Phillips and Dan Evans.
I understand your point that the Royals, Pirates and Brewers are examples that things could be far worse for the Reds. JimBo probably has the skills to prevent that kind of debacle from happening in Cincinnati. Yet I no longer hold out much hope that he's got the vision and ability to make the Reds a substantially better team.
The ugly truth may be that the Reds need to cut JimBo loose and suffer under the yoke of a can't-do ownership/GM combo for a few years before something better rolls into town.
There will be a post-JimBo era and no matter how unpleasant it might be the JimBo era has flagged enough that I no longer see much of a reason to forestall the future.