The Miami Dolphins have not won a football game in San Diego since they were coached by Nick Saban. That was, as you probably recall, some years ago. By almost any measure, the Chargers are a more talented football team than the Dolphins. It's possible that Adam Gase is a better head coach than Mike McCoy just based off how little we have to go off with regard to Gase and McCoy's terrible track record. At most other positions, the Chargers are as good if not better than the Dolphins.
At the most important position on the field, the Chargers are vastly superior. The comparison between Philip Rivers and Ryan Tannehill is laughable. Rivers is likely a future Hall of Famer unless voters hold the relatively low quality of his teammates against him when it comes time to vote. Tannehill is a converted wide receiver that still looks like he is never going to take that next step.
The Chargers are also playing at home and traveling cross country is rarely good for teams. This game has a chance to look like the last time the Chargers played a home game against a team from Florida.