https://nudges.files.wordpress.com/2008/06/mpg-graph.jpg
If an average driver (12,000mi/yr) switches from a 12 mpg car to a 15 mpg car, they save 200 gallons of gas per yr.
If someone who drives the same distance switches from a 60 mpg car to a 63 mpg car, they save 10 gallons of gas per yr.
If someone who drives the same distance switches from a 133 mpg car to a 141 mpg car, they save 5 gallons of gas per yr.
In addition to aerodynamic improvements (which is of course a non-trivial engineering effort), Tesla does have a unique rear motor design that is more efficient, an industry-leading inverter design, and many incremental engineering efforts that cumulatively save several percentage points. Because they are "all-in" on an EV design they don't have to compromise because of a shared EV/Hybrid vehicle frame design for example.
The EPA listings also provide kWh/100 miles which I use for comparison to avoid the unfair MPGe equivalency.
Another example: the Hyundai Kona is a purely electric platform that doesn't need to compromise, and it matches the efficency of the Model Y.
The Ioniq has substantially less range than the Model 3, and is a much smaller car. If the Model 3 still gets slightly better MPGe despite those differences, I'd say Tesla still has a pretty significant efficiency advantage in this comparison.
So they've sacrifised range by installing less batteries, gaining more luggage space, lower weight and lower price.
The Hyundai Ioniq is a similarly shaped EV as the Model 3, and it gets very similar numbers - 133 MPGe (Ioniq) versus 141 MPGe for the best version of the Model 3 Standard Range, a difference that's smaller than going from 18 to 20 inch rims on the Model 3 Long Range Performance.
It is essentially useless to compare cars that are within 10 MPGe of each other at 130+ MPGe. If your tires are slightly off optimal pressure, or you've left something heavy in the trunk, or you've chosen different rims than standard, you've lost more than this. God forbid if you've put on a roof rack, probably drops you 30 MPGe down to 100-ish.
This discussion also underpins why MPG is a poor unit to measure efficiency with. The inverse measures used in Europe like L/100km or kWh/km are much easier to compare, as differences can be compared directly between a low and a high efficiency car