Each district is its own. Pelosi would never be elected in Florida. Cruz never in New York. To compare all using an overall sum quantity is ludicrous.
I can name several seats in FL that would elect Pelosi in a heartbeat.
Also, the house popular vote is very important. It is why I could tell you the Democrats were going to take 40ish seats in the midterms based on what we were seeing in the generic ballot polls. Besides that, house seats are highly correlated. If you see polls in a couple seats, you can use those to get an idea of what is happening in similar seats across the country.
If Democrats carry a national vote by 8%, they are going to win the electoral college regardless of anything else.