I doubt it's a competition to find the DBA who makes the best powerpoints presentations. It's more likely that someone higher up wants to review you before hiring, and that HR know that person will push back against hiring you on the basis of your presentation looking rubbish. If you're going to be presenting to clients then it could be a valid point but that's unlikely for a junior. It's more likely that the higher up person is just wanting to make their mark on things.

That will probably happen a lot in the job...