AD has had exactly 1.5 games at #13.
It looks promising at best.
That isn't to suggest I don't think he shouldn't be signed. I think Doueihi is a great player & have championed him often.
BUT.
An extra option to play #13 is required AT LEAST in case Doueihi doesn't continue to look promising at #13.
What I think we have seen is, the guy playing at #13 has to play direct, play one off the ruck & be able to pass before the line, while holding up in defence. This allows Luai & Latu to shift a little wider if they choose while still keeping a threat close to the ruck.
I would argue that Terrell May actually plays that role a little bit already, a bit like how Payten used to. His pass selection feels a little forced at times, but he certainly seems to enjoy the pass before the line.
Certainly sink some money into Doueihi. Have May practice a little of that role himself. Add a front rower that adds something to the squad (size, speed, aggression etc...just one of these things is enough). I've suggested him a few times, but Freddie Lussick could play the role out of #14 as well as cover #9- it's what he's been doing for the Warriors KOE. It gives back-up to Doueihi & May as well.
Elliott from the Knights would be an option as well, but probably more if Doueihi moves on. I assume you spend similar contract values on Doueihi & Elliott.