I mean, we only see the one city. It's like seeing a small "country village" and assuming the rest of Earth is the same.
Have you ever seen
Stargate (any of it)? In the movie and lots of episodes from SG-1 and Atlantis, we see a lot of alien worlds that are a mix of "old-school village" and highly advanced technology bordering on "magic." That is the vibe I got from the city in
Covenant. Given they have a fleet of Engineer ships under the city, it suggests they are absolutely Engineers. Then there's just the question: homeworld or colony? As for everyone coming out to welcome the ship: maybe they're like, "Hey, we never heard from these guys 2,000 years ago. They're alive!" Happy greeting until the black goo drop.
Planets are big. Maybe the city David came across was a "smaller settlement?"
Does Prometheus/Covenant play a big role in Romulus beyond "look, black goo?"
I hate it when sequels ignore sequels. Terminator has been bad at this.
Ridley's films ignore AVP.
Romulus acknowledges black goo, but otherwise "moves on" from the prequels.
TV show: ignoring AVP and all 3 prequels?