the point is that it isn't higher cost for those missions. Falcon Heavy will have to run at 100% expended mode which is nearly the same cost as Vulcan.
And some missions and payloads outright exclude falcon Heavy, period. High orbit and/or large satellites.
they can compete in very specific cases - like heavy load to GTO. Falcon Heavy would require full expenditure of all 3 cores to match, which wouldn't be much cheaper. Plus the larger fairing size helps with certain kinds of satellites.
in terms of usage though, they are quite similar. Coal serves on-demand power, whereas renewables generate power at times that don't always align with demand. Batteries can take the role of a coal plant if the renewables already generate sufficient energy, just at the wrong times.
Severing one of those undersea fiber optic cables