Whilst I also want an accurate count, we are assuming that the old count was accurate and the new count is too generous. It's possible that the old count was too harsh, and the new count is accurate.
When compared to Strava, Nike and MyFitnessPal, the Apple Workout app already grants fewer calories per exercise than these apps. MyFitnessPal app (somewhat ironically I guess, for a calory counter) is by far the most generous of the apps. Nike is somewhere in the middle, and Strava isn't particularly generous or harsh in its count, but it is by far the most simplistic of them all - an average sized male of an average height and weight burns almost exactly 100 calories per km of running.
So if Apple has revised upwards, then they are just trending towards what everyone else has. Of course, calory counters, especially off of a heartbeat sensor on the wrist, are generally inaccurate anyway and you should only use this as a guide.