Those of us in the position I'm in would be perfectly happy to accept a battery pack capable of actually producing the 691 HP if Tesla were capable of providing it. I'm guessing that based on what you wrote above, if Tesla announced tomorrow a 110 kW pack that would be capable of allowing the car to produce 691 HP, you would not believe that it would be appropriate for Tesla to replace our packs with those because we'd be getting the benefit of "betterment" in the form of increased range, right?
It seems to me that common sense would dictate that if the only remedy that is capable of undoing the injury available to the injured party has a side benefit of betterment, then the injured party should be allowed to benefit from this betterment, since it is the best option. In my example, Tesla winds up resolving the problem, and supplying some extra range in the process. That would seem to leave the customers closer to what the goal of purchasing the car was than forcing them to return the cars. Since it was Tesla that was culpable, a solution along those lines would seem appropriate, from a common sense standpoint, but of course I am not a lawyer.