My understanding is that most of the modern research has generally advised against the idea that Toba caused a population bottleneck. I'm not sure there's any archaeological evidence of any hominid settlements that were abandoned as a result of the eruption--and there are several sites that demonstrate continuity through the eruption. Furthermore, better constraints on the date of the Toba eruption appear to put it after the onset of the glacial period.

So the theory that it caused a severe bottleneck is something that I'd consider 'discredited' rather than 'disputed' or even 'controversial.'