Everything you've identified here is very much an intentional feature. Jump height is explicitly randomized, being killed instantly upon level start is a hilarious joke (and doesn't really impede you in any way; dying 10 times is essentially identical to standing still for 5 seconds), and fish speeds are also explicitly randomized, presumably for the exact purpose of making it harder to learn how to avoid them.
These features are all there in part to push on and play with standard ideas about "bad game design"; you can read some things sylvie has written about this e.g. here http://sylvie.zone/posts/2021-02-15-Sylvie-A.html and here https://twitter.com/sylviefluff/status/1282834519880544256