When on a trip, you are charging in order to be able to drive. MPH is the only meaningful charge metric relative to trip charging when comparing vehicles. I don't care in the least whether other vehicle X charges at a higher power rate than my vehicle for the purpose of comparing charge speed--I care how long I need to charge in my Tesla vs in the other car I'm considering.
And when comparing how long I need to charge, I'm going to calculate how long I need to charge in order to make the next leg of the trip--in other words, how long to gain a certain number of miles.