Yes, I think we established early on that it DOES have an effect. You are absolutely correct that the rake is designed to help with efficiency. The subsequent responses were addressing the extent of that effect.
I like the idea of a cost analysis too. Using the industry standard 12,000 miles per year, the current average fuel cost $3.38 per gallon (as published by eia.gov for 11/29/21) and the advertised 15 cty 20 mpg hwy (as published by FCA on the window sticker) we can calculate the cost of losing 1 mpg.
12000 miles / 20 mpg = 600 gallons of fuel used per year. 600 gallons x $3.38 = $2,028 per year.
12000 miles / 19 mpg = 631 gallons of fuel used per year. 631 gallons x $3.38 = $2132 per year.
Therefore, a 1 mpg loss from the advertised 20 mpg will cost you $104 every year on average.
Since nobody drives entirely on the freeway, we should also look at city and combo.
12000 miles / 15 mpg city = 800 gallons of fuel used per year. 800 gallons x $3.38 = $2704
12000 miles / 14 mpg city = 857 gallons of fuel used per year. 857 gallons x #3.38 = $2896
If all your driving is in the city, you pay an extra $192 per year if you lose 1 mpg.
And finally since a realistic analysis would be a combo of both freeway and city, I'll use the advertised 17 mpg for a baseline.
12000 miles / 17 mpg combo = 705 gallons of fuel used per year. 705 gallons x $3.38 = $2383
12000 miles / 16 mpg combo = 750 gallons of fuel used per year. 750 gallons x #3.38 = $2535
The cost of losing 1 mpg is $152 annually, assuming average mileage, average fuel cost, and combined driving conditions.