There's more issues than that to the General.
While a lot of folks don't actually want to face it, folks feel like they are just banking on the idea that some Republicans might vote for Biden.
That said, I'd say the reasoning there amounts to a "Coin Toss..." I get why they buy into it, but I have my doubts about if it actually goes that way.
- Actually being able to get the "Nuts"/"Bolts" done in a General. While he has been passable during the primary so far, what has pointed to that he that it is even likely that he could. While I don't think that he is as dull as some folks in cable news have suggested(he's seemed sharp enough in interviews), is he sharp enough not to come up for the bait if he is running against Trump?
That's where I get worried. This guy is out there challenging voters to push up contests.
- Does Biden have an actual argument that is going to seem far enough away from "More Of The Same..." to make a difference in swing states? While I get the doubts about Warren or Sanders, you cannot reasonably suggest that they don't have the argument and that it's down cold.
- Trump isn't just running for a first term this time out. If Trump doesn't just completely face plant, can you make a case against sticking with him? Again, Warren or Sanders have that case. I haven't seen Biden really make it yet.
Never mind the built in weaknesses that Biden would have. Folks will talk all day about Sanders being potentially weak, but I don't think anyone is seriously thinking over if a Biden General Election run can be pulled back onto the road if it starts heading for the ditch.