Correct on the battery pack size vs accessible kWh. The numbers I quoted were what is user accessible. The pack on a Mustang Mach E has more capacity than what the user can access.
From what I can tell, Ford tends to be more conservative with estimated range (meaning it generally can drive longer distances than advertised), but I think the climate harsh winter weather will severely limit the range. I would also add that if it is too hot, that too will limit the range. Ford does this to enable the battery to last longer. The chemistry in these batteries are lithium ion. They will last for a very long time if you keep the battery in the range of 80-90% maximum charge and 20-25% minimum state of charge. Charging it to full and draining it to empty as a regular routine will much more rapidly degrade the battery capacity.
Another factor that impacts battery life is how fast and how often one uses DC fast charge. Filling the car up with high current will degrade the battery faster. Using DC fast charge all of the time will also degrade the battery life. The Mach E also slows the rate of charge as the pack gets closer to full.
From what I understand Tesla range is more optimistic on how far it should go on a charge relative to Ford. Tesla has a robust charging infrastructure, but they are less concerned about battery management and warranty and leave that to the user to decide.
I have heard from some Mach E owners in extreme cold that their range plummeted radically in the sub freezing temps this winter.
Battery chemistry and types along with active battery cooling and management also impact all of these factors.
I know it is a fair and reasonable "simple" question, but unfortunately I see this as having a very complex and variable answer. The term "your mileage may vary" absolutely applies here.
Now when it comes to your question of counting on a Mach E to go 500 miles on one charge without stopping...I don't see that being practical now or at any point in the next few years at least with almost any BEV including the Lucid Air. Lucid Air is claiming that range because they have a more aerodynamic sedan, with a larger battery pack. I have no idea how realistic or optimistic they are with their range estimate. I think one will have to stop at least once, but probably twice to do at least some charging. I don't think you should let the pack capacity drop too low or slam it to full all the time, let alone on a road trip.
Our goal is to expect our cars and battery pack to last for a very long time. We are still driving several days per week our factory built 2002 Toyota Rav4EV with 118K miles and a battery pack that was made in 2002 (I had an opportunity to get a lower mile pack about a decade ago, but it is still with batteries that are almost 20 years old). That car is fine for one of us doing local errands as it "only" has a range of 80+ or so miles, but we rarely drive it more than 70 miles on a charge and usually 20-40 miles on any given day (we are not driving as much as we did pre-covid). A modern EV with a 250+ mile range will be ideal for how we live today.
I think at least one EV in a multi-vehicle household with a 200+ mile range for what most people do with a car drive it 40-120 miles per day with a road trip 1-2 times per year is what today's EVs are really optimal for today in 2022.
What they did in Norway is accomplish 500 miles of range...but it is an outlier and not an example of practical or "real world" driving. It shows it CAN be done...at least technically. I do think that depending on what model of Mach E is chosen and moderate driving during the spring and fall mild temps one can go about 300 miles on a charge, but I would think that stopping closer to every 200-240 miles is likely to be expected. That is just my opinion, you may find others out there that will say otherwise (maybe better or worse).
If the primary use for the car is weekly long distance driving, I personally don't think an EV is the best choice with the state of the infrastructure and battery tech in Feb 2022. Tesla is ahead on that race as of today because of the Tesla charging infrastructure, however, all of that will change over time.
Our next EV (#6) will be a Mustang Mach E GT Performance (whenever the shipment of chips can complete the build on our car that has been in production since January 15th). This car we think will offer us a fantastically practical vehicle for how we live every day.