So how, if even possible, do I correctly determine the bitrate of a
video if it seems excessive?
There's not a "correct" way. That's why every encoder you come across presents bitrate as an option to the user. The visual complexity of every video is different, and visual tolerance levels of artifacting is subjective in every case. File size vs image quality will always be a tradeoff, and it takes an informed human being to decide where that tradeoff is most acceptable.
But to focus more on the "how" one best makes this decision, there's not much to say other than: trail and error.
You can bifurcate. That is, pick a high number, try it, pick a low number, try it, then pick a number between whichever direction was more suitable, rinse and repeat. It's still a subjective process. If you search the internet, it's not hard to find ballpark ranges to get you started, given the specifics of your output requirements (resolution, framerate, etc). When you do this, you should use a representative subset of your total output to test, so that you can iterate more quickly.
Also, be sure to consider your destination platform. You don't mention it in the question, but it will affect your decision. If you're delivering to bluray, for example, you have a hard limit on total file size, and you'll probably want to optimize quality for that specific target. On the other hand, if you're delivering to an online streaming service, you might want to go for maximum quality because YouTube, Vimeo and the like will automatically generate lower-quality versions to serve to people with slower connections. Conversely, you might value high-speed upload for quick turnaround times. Only you can decide.