I think he is serving as cannon fodder for the Defence's more controversial bits of evidence, that is, the bits that the Defense couldn't get a real professional to stand behind/risk their reputation on.
Secondly, and less importantly, I think he has been put on the stand (unwittingly) to probe and extract more of the prosecutions case by proffering opinions on subjects and evidence out of his depth, to which the prosecution must respond.
As you know, the prosecution has revealed very little by way of narrative at this stage. Further, we have only heard a part, albeit a large part of the ballistics report. The bedroom door holes have not been discussed at all, yet they have been entered into evidence via photos. And let us not forget the 5th cartridge case that Nel mentioned without correction from his team, the defense or the judge. That cartridge, if it exists, could be in one of the many photos logged into evidence.
I still think they will haul out their ballistics "experts"
Further, I think we will hear more from the blood splatter experts, but not before Professor Dixon has offered his learned opinion