A lot of that is posturing but there is truth to it. Trump has huge support among Republicans/his base. I just went through the 2016 election archive, lots of similar state poll and NPV margins, lots of people saying Trump would be defeated in a landslide.. and look what happened. Hillary lost all 6 states that Obama carried TWICE and showed significant polling error. Not to mention, she almost lost New Hampshire, Nevada and Minnesota. Don’t be complacent and the Dems should of picked a better candidate.
This time, if Biden loses but the Democrats keep the house and keep the senate close, that's what the narrative is going to be. That is they pick poor candidates. If Republicans just sweep everything, even by very close margins, the narrative becomes that Democrats don't have enough votes. Period.