Hitchhikers are more likely to come from coral additions than live rock, as distribution and better shipping conditions guarantee more biodiversity.
The shotcrete installations I've done become covered in coraline algae in about six months, but just one type. Live rock will have at least three colours of coraline as well as countless other varieties of microfauna (probiotics). Reef ceramics are comparable to dead rock, but without the buffering capacity. Did you have a lot of diatom issues for the first few months?
Your tank looks great, but it takes longer to get there, and there are no pleasant surprises. On the positive side, there are no unpleasant surprises, other than cyanobacteria, dinoflagellates, and diatoms.