The weight makes a big difference because you pay by weight for something you think you may need but weights nothing.
If that diversity must come from the ocean, how much of the original diversity will still be in place after being harvested, stacked in the open air, hosed down and stripped of most growth. Then packed and transported in open air. All the time in contact with local competitors. If by air transport without pressurization. How most cells having lived at a constant pressure below surface will survive, from those who have survived the voyage to the surface and first contact with direct sunlight? After arrival how the survivors will compete with active local clades wanting the same thing? What will be left of the original diversity? Not much.
The myth of "live rock"
if you want diversity from the ocean go and collect 5 grams of local growth ( algae) and sand from the reef, do it in a 1.5 l bottle, close it below the water surface and cover it from sunlight, keep cool ( room temp) in the dark and have it home within 24h in your cabin luggage. Then maybe 1% of the original diversity survived,feeding on the other 99% But why?
Every organism added to the tank does contain its own holobiont full of essential diversity. Real live rock is entered with each piece of coral, with each grain of sand.