Some H.264 videos that I have seem to have excessive bitrate, is there a way to determine/find their recommended bitrate? So I have some videos that are Full HD, h264 but they have over 30M bitrate at 30 FPS, they are SDR and their quality is not very impressive so it seems excessive and unnatural for such unimpressive quality - I have seen much better looking h.264 content with 60 fps with even half of this bitrate. So what I did try to do is use -crf 17 (yes, without encoding), to see how much this will reduce them and it usually does do a good job for example it made the file to about 12M, I also tried -fs with even a higher number of size than the original, and it brought the file down to 5M bitrate, I don't know what actually happens behind the scenes with this, but I think the video looks a bit worse, not much though compared to the 30M that it was.

So how, if even possible, do I correctly determine the bitrate of a video if it seems excessive?
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.