As I’ve said elsewhere, raw bitrate means exactly the same between them, because the bitrate is the number of bits per second of video after compression. What you mean is that you set a target bitrate and the different codecs have varying success in meeting that target. You can use two-pass encoding to improve the codec’s accuracy.
But what matters is the average bitrate required by each codec to achieve the desired level of video quality, as perceived by you. The lower bitrate you need for the quality you want, the better the codec is.
I’m not saying it is the size of the file, I’m saying the bitrate multiplied by the number of seconds determines the size in bits of the file. So for a given video duration and a given bitrate, the total size (modulo headers, container format overhead etc) is the same regardless of compression method. Some codecs can achieve better perceived quality for the same number of bits per second. See. e.g. veed.netlify.app/learn/bitrate#TOC1 or toolstud.io/video/bitrate.php
If it’s compressed to 6,000 kilobits per second then ten seconds of video will be 60,000 kilobits or 7 megabytes, regardless if it’s compressed with h.264, h.265 or AV1.
That makes no sense. The bitrate is how many actual bits per second the data uses after compression, so at the same bitrate all codecs would be the same size.