I was using Vim for a few years and later switched to Emacs. Both provide commands for handling indentation of lines and blocks of code. You just paste and select/mark a block, then indent or unindent until the first line of the block is aligned with the preceding line in a place where you pasted the code. It's true that you can't auto-indent on paste, though. Still, it never slowed me down noticeably. It's a trade-off, to be sure: you need to align indents manually, but then you don't ever have to deal with things like this:
Yeah, the thing is, if you do forget to align things, which is a thing if your eyes are not the sharpest, weird things can happen, especially when you are writing scripts as if there's no tomorrow. Those experiments usually end up being written for the node.js runtime because I really, really hate aligning lines when I'm writing one-off scripts.
Well, Python is in general not the greatest language for one-off scripts, so it's not strange to use something else for this use case. I definitely never felt your pain, though. I think I'd have to see you edit a Python file live to understand what makes it problematic for you (for example: what width of an indent do you use? wouldn't increasing the width help you notice misalignment? and if it's about seeing/noticing, can't you make your editor display whitespace?).
In my experience, there's no syntax that would be free of gotchas and pain points - I tend to accept them, and if I'm going to work with a particular syntax more than once, I write a bit Elisp to make working around them as seamless as possible.
I totally have this problem with yaml. I wish vim had a line-these-things-up button, kinda like how % lets you bounce around in parenthesis - something like that for leading-whitespace alignment.
