I disagree. I think the better way to think about the HO is that they spend the first half of the game searching and preparing for the third promotion, which is like a sudden discovery of mini, but supercharged, natural wonder tiles. Sure the tiles are very weak initially, but your goal should be charging them up.
Ideally, you would have a core of cities generating as many great people as possible, and also have a massive colonization effort to claim leylines as early as possible, especially the ones in deserts and tundra which tend to have more workable in an area.
The beautiful thing about the leylines is that they don’t need a high population or district infrastructure in their city to benefit from. A 2-pop city that can work 3 15+ culture/science tiles (counting city center) is very powerful. You could find several of these out in the tundra. If you go for engineers, these tiles can also add massive production.
The way I see it, their first promotion is meant just to help you find them, not getting the adjacency.
The second promotion is meant to help generate GPP for the third promotion. Everything leads to that third promotion.