Having done my railway conductor training, I can say confidently that people just don't understand how long it takes to fully stop a train moving at that speed (it takes over a km and up to 2km sometimes depending on the amount of weight) . Furthermore, the train slowing down wouldn't really be felt in the video due to how long it takes. You also wouldn't hear the brakes from the front of the locomotive because they are all behind you and there's that huge diesel engine between you and all the brakes. Also, the diesel engine is not what is driving the wheels so there wouldn't be a very noticeable change in the rpm range of that engine like in a car. These locomotives are diesel electric, the wheels are being driven by big electric motors. the engine is just a big generator.
One more thing people don't realize, it's illegal to put a train in emergency braking unless it's absolutely required. Wildlife is not one of those reasons (neither is it for a car on the rails until you actually make contact). If the train was carrying dangerous goods (which most do), putting it into emergency braking could derail cars and cause a much bigger disaster. Some of the stuff trains carry is so dangerous that it's the only way to transport it (as in you can't transport by air, or road because of the greater risk).
Yes it sucks that this happened but it certainly isn't what they wanted if they could've done more I'm sure. We'll have to wait on the investigation and the review of the black boxes to see if they were trying to slow down or not. I'm pretty sure they were trying though. They were probably pretty heavy and in winter time it takes even longer to stop.