You buy space in Equinix DCs because they are network neutral and have a high density of ISP POPs, i.e you can light up fibre between your cage and HE, Level3, whatever other transits you want to use + peer with everyone on the local peering fabric super easily.

I consider Equinix transit to be an option only when you really can't be assed to do anything else and you don't intend to hammer the links anyway, otherwise yeah you should be doing all the things above because otherwise you could have rented colo in some shitty backwater DC instead.