I think Hikaru has a relatively high ceiling - there's at least a plausible chance that his 2830 performance rating at the Grand Prix is actually reflective of his current playing strength, and that he'll keep it up at the Candidates - and at those odds that may be enough reason to count him as a good value bet.
Of course he also might make the Grand Prix look like a fluke, and play the way everyone expected a retired streamer to play, and get kind of crushed. But that's a normal risk on any longshot bet.
I will push back on any claim that anyone is "virtually guaranteed" any finish. I think everyone in the field could finish in almost any spot and that this is a super wide open event. Not to say that there aren't favorites and underdogs, but there are no locks and nobody without hope imo.