I think 'his stock is maybe higher' because when he came in to the team, he was individually good while most of the rest of the team were actively bad. It was also genuinely impressive at how quickly he stepped up to test level given how young he was at the time.
It also depends on how you're defining risk. Given the context of the comments here, I think we're mostly talking about it in an attacking sense.
He's only just turned 23 so he has plenty of time to add to his attacking repertoire. Moreover, I think it's a little unfair to criticise him too much for not hitting the line more etc. when his main role has been to chase kicks. While it does maximise his skillset under the high ball, it also hasn't allowed him to do much else in attack.
I actually think the risk is higher from a defensive POV. IMO, working on his positioning and being very slow on the turn are the things he should be prioritising. If we're picking him as the safe option, that needs to apply to more than just defusing aerial bombs.
If we're looking at Furbank as his principal rival this season, it's an uncomfortable comparison. They're totally different players and who is the best choice is really dependent on how we want to play. There's no point in picking Furbank if the main tactic is chasing kicks just as picking Steward as a second playmaker isn't maximising his talents.