Until names are added to the “generic ballot”, the ballot will alwys reflect current popular opinion.
When names are added, the numbers will often shift . . . . sometimes better for the “good guy”, sometimes not so good.
Sure, each race is different. The reason people focus on the Generic Ballot is that for the House races, there is very little polling, at least public polling, going on. So in order to get an estimate, they look at this. Some Dems will campaign better than others, or will not have strong opposition, etc. But in the end, if a GOP candidate campaigns well and doesn’t blow bubbles with his drool, he should do well.