It depends what the parameters for rivalry are .. a ground-based telescope can take multiple photo's, perhaps even thousands, at very low cost - although the resolution may not be comparable, this doesn't discount the value of the data to the scientists who are obtaining it at a far greater reduction of cost and effort than those who rely on space-based instruments. Remember, we don't have a permanent instrument stationed at Io - these spacecraft are doing fly-by's and thus have a limited window of opportunity.

So, while the resolution may be great eye-candy, the consistency of the data over time is vastly different. "Higher resolution" does not always mean "better science", especially if its a one-shot compared to thousands of data-samples...