Yeah, Smackdown is weak on heels. Aside from Roman (who is obviously on hiatus), AJ is the only heel former champion on Smackdown so is the obvious first challenger for Cody and so a theoretically credible threat (although not really). While I do think the better idea would probably have been have Santos win at Mania and then get the title shot, given the Mania results, this is the most sensible decision.
As for those tag titles magnificent. Honestly, I didn't realise how used to bad tag titles I was until seeing the updated belts where they're absolutely stunning instead of incredibly generic.