They seem quite sure of a Biden victory, nervous, no. Overconfident? Possibly...
I agree with that for the most part. We've also seen that in 2020 while Biden was predicted to win in many states, he eventually did win most of them but not by the margin that was expected. A similar thing might be happening here,
however I feel like the Sun Belt states for some reason at this point are shifting quite a bit to the right and might be moving into Lean R territory. Lean R still means that Biden can win them if the situation is the same on election day (Michigan & Wisconsin 2016 were also Lean D and Trump won them), but I think something more specific is happening in Sun Belt, which might be related to demographics (minorities, urban population) and maybe its institutionally more conservative character (like on abortion), but also that there is more economic hardship there supposedly. I don't think it's impossible that AZ, NV, GA and NC all don't end up being (very) close at all.
But it's the Rust Belt trio that will likely decide the election and my feeling says it's toss-up/tilt R at this point. I suspect the polls will improve a little for Biden simply because there's more room to grow. All Trump needs is 1 state but Biden might end up winning them all three and deny Trump which seems to be the most realistic scenario for a Biden win at this point. A classic blue wall holds electoral victory.