I’d say this is more of an argument against camelCase (which does indeed suck in terms of legibility, especially compared to the much_more_readable_snake_case).

That font in particular yes, but proportional fonts are faster to read.

I think anyone can notice it if they try. BTW, there is a study suggesting we start reading noticing the shape of the word envelope. If that's the case, that could be one reason

What a terrible alternative though

Is the goal to read text or code? I need to be able to tell what's a space between variables and what is camelCase

What's up with the whitespaces in the second font. How can you tell what is even a whitespace there.

Uppercase letters have left padding, which is 1/3 of a whitespace char. I got used to it within a few minutes.

That padding is for helping with camelCase, but another opinion is that snake_case is better than camel. Better yet, some languages allow them in identifiers.