I don't think the weight of the cars is necessarily a significant issue as long as the track is in good condition. If there is a rail defect, of course, the heavier the train rolling over it, the more likely it is to fail.
Aside from that consideration, I would say that the length of the train itself is a far more serious problem, for two specific reasons. One is the problem with streamlining that apparently you mentioned in your report: a train tends to want to straighten out the curves, and the longer the train, the greater that streamlining effect. When a derailment is caused by streamlining, of course the longer the train, the more likely that is to occur.
Another problem with train length actually also relates to some extent with the issue of dynamic braking. It is that many trains are poorly marshalled. For purely safety considerations, the ideal way to run a mixed train is with all the loads marshalled ahead of all of the empties, because it's the best way to minimize excessive slack action. Again, excessive slack action is itself a dangerous condition. When you have a mixed train, the longer the train, the more difficult it is to control that excessive slack action. Of course, a simple solution would be to insist that any train leaving a major terminal have all the loads marshalled ahead of the empties.
With respect to excessive slack action, dynamic braking is an extremely valuable tool in controlling train speed, but it also has an ancillary effect in helping to reduce slack action, because if you're going down a grade and you're completely controlling the train just with your dynamic braking and perhaps an occasional minimum application of the train brakes, then the train stays bunched and there is essentially no slack action occurring. However, when you don't have dynamic brakes, you have to first of all, before you can even apply the brakes, stretch it out, so that when you do apply the brakes, you don't suffer severe slack action that may cause a derailment. Then once you've applied the brakes, eventually it smooths out, and now there is no slack action.
Then, if you have to increase the brake pressure.... Of course, once you release the brakes, all that slack action will start to happen again, with the possible exception of unit trains, but on some cars the brakes release faster than on other cars, so you're getting all that slack action activity. Dynamic braking is also of tremendous assistance in controlling excessive slack action.