The charge rates sound similar, but somehow I feel the charging time is almost half: 20-80% SOC in maybe 25 minutes?
I do agree that legacy S/X DC fast charging rate for 20 - 80% is noticeably slower than that of what the newer cars (S/X refresh). Hard for me to put a number to it.
I guess that's where the total range and kW/mi needs to be factored in. So to simplify it, we could just consider miles gained from 20-80% and leave consumption out of the picture, since the guessomter in theory takes takes care of that.
I think the perspective of owning the vehicle and every car's efficiency has to be taken into account when making the comparison. It's not exactly an apples to apples comparison between a MX and M3 for instance. Both are different segment cars, with no-matching aerodynamics, weights, payload capacities, battery sizes etc.
My range is about 260 mi (rated 272 when new), so my 20-80% would be 206 mi in ~25 minutes.
I think the best way to look at it for a suitable comparison is to consider how much 'effective energy' has been put in the car's battery. By effective energy I mean the actual kWs of electrons added to the battery which translate to the number of driving miles gained (depending on the non-variable factors such as car's aerodynamic efficency, empty weight, wheel size, tyre profile) and variable factors such as battery capacity and degredation, driving style, external conditions (weather, traffic conditions, speed, acceleration, number of passengers and payload) etc.
E.g. for my MX the 20 - 80% charge adds approx. 52 kWh of energy in the battery. That gives it a rated range of ~145 miles since the car usually averages about 360 Wh/mi (normal driving conditions i.e. relatively flat road, no strong headwind, 22" wheels, normal driving style and climate control on).
I would assume that your 2023 M3 RWD would be able to input more 'effective energy' in the car's battery due to it's better charging performance as well as favourable non-variable factors. This would, in turn would show a greater number of 'miles added' to the battery as well since M3 RWD is a far more efficent car than a legacy MX.
The miles of range shown in the car's instrument panel is merely a representation of the average of the non-variable factors and variable factors over the course of a time period. Essentially the car is trying to make an educated guess on how many miles the car would go typically with the amount of kWh added to the battery back based on historical average data.
Can't guess at your range, since it's model dependent, but I can see that your range may be similar with a 100D.
Mine is a P100DL, which has a range typically about 10% lower than that of a 100D.
So maybe charge rates are similar, but miles gained are much less because of consumption diffeence bwwteeen the X and 3. ?
I think the average charge rate to input the same amount of kWh, for a certain range of kWh into the battery would be faster for a M3 RWD. For example, M3 RWD comes with a 57 kWh useable battery capacity and assuming 0% degredation (just for maths), a SC session (V3, no stall sharing, battery pre-conditioned, 85F temperature) 20 - 80% charging would add about 35 kWh (from 11 kWh at 20% to 46 kWh at 80%).
This would definitely be faster than the 35 kWh added during the 20 - 80% charging of the MX's SC session (V3, no stall sharing, battery pre-conditioned, 85F temperature). However, these 35 kWh will only take the MX's battery to about 55% SoC (assuming 0% degredation for maths and a 97 kWh useable battery capacity).
So, the legacy MX would not only be slower to add the same amount of electrons in kWh terms due to older and slower charging technology, but also it will take longer to charge from it's own 20 - 80% SoC since the battery size is larger. To top it off, it will also show less 'miles added' because it is a bigger, less efficent car than a M3.
The perspective of owning the vehicle and the owner's vehicle use case eventually matters a lot when considering charge rates, miles of range etc.
