Teams that don't take the break will be inhibited by the limited range of their un-recharged vehicles. Are you suggesting that some people will find out how to swap their vehicles, and keep the shift going? (Or add an extra length of hose to the fuel line, for a virtually bigger tank? That type of trick isn't going to work well with battery vehicles...)
How is it you propose that someone is going to get more work done in less time, when their total range / route length is reduced by the extra effective distance they would have been able to continue with 15 minutes of fast charging added in, at the one or two points where it makes sense to add a stop in their shifts?
Then, later, they would find that the newer batteries actually can get by with smaller breaks. Or other efficiency gains that we just aren't thinking about.
My point wasn't that it would fail immediately, but it would eventually.
By throwing the furthest of their deliveries into the nearest lake, and coming back early with an empty truck and charge remaining.
Drivers don't want to sit around waiting for a recharge. They want to clear the truck and go home.
If the trucks go far enough, and the drivers don't need breaks, then say that I guess. Drivers don't want to do their job is not an engineering problem, whereas delivering more packages per shift could be one.
You can see this in long race formats that have breaks. Teams that find a way to not do the break wind up winning. Such that you then have to mandate them, which works for things that people don't get value out of.
We already have similar mandates for truck driving, and I think most folks would be surprised that that exists. And they are far looser than what would be required for last mile driving.