Laxalt (or possibly Lake) was the one whose chances of winning were most overrated in retrospect, but the one whose overall amorphous "quality" was the most overrated was clearly O'Dea. I would say Smiley, but nobody seemed to rate her so much as they underrated Murray.
This is the correct answer.
Laxalt was overrated the same way Ted Budd (who no one here has brought up, interestingly enough) was overrated — (a) both Laxalt and Budd looked (and indeed
were) more 'generic' next to more 'controversial' and inept Republican candidates, but they both embraced Trump and never really put distance between themselves and the national party; (b) many (myself included) just generally overstated the Republican lean/trend of NV and NC, but that had little to do with Laxalt and Budd as candidates; (c) many who overrated Laxalt and Budd really just underrated Cortez Masto and Beasley, who were arguably (slightly) stronger than generic D, at least with the benefit of hindsight.
However, many of the same users who used to point out how overrated Laxalt was also pointed to Joe O'Dea as a prime example of an 'actual' strong challenger not tainted by Trump and the toxic national party who would overperform in a way more 'partisan' Republican candidates in the swing states would not.
No one expected O'Dea to lose by more than Trump! As 'overrated' as Laxalt and Budd were, at least they didn’t perform worse than Trump.