Honestly, I don't even remember. It was something to do with minor differences in the cursor movements of specific commands.
Anyway, it's been years, anything may have changed in the meantime. I should probably give it another go, those were simple nitpicks that I was too impatient to tolerate.
have to be relatively fluent in Vimscript to pull that off
I don't think so, using ALE just requires to install the plugin and the external programs that it will interrogate. I know almost nothing about Vimscript.
thoughts regarding Vimscript
From what I've seen it's a scripting language like any other, but one that is extremely specific to vim. The syntax is also quite different from anything else, so I never felt the need to learn it.
Neovim
As a general concept, it seems a good idea, I also know Lua so it would seem to be a logical switch for me.
However, during these years every time I tried it it had some slight differences from vim that made using it somewhat annoying. Moreover, it never seemed to provide such a better experience that made me switch permanently. I'd like to like it, but I never had a reason to.
I'm a bit surprised that no-one mentioned ALE. If you want to turn vim into an IDE it goes a long way.
Having the compiler warnings/errors inside the buffer is already really useful, but then you can also add LSPs and there isn't really much missing. I've recently developed a Java program entirely in vim using Eclipse's LSP.
You should put some quotes where you use the array:
not_what_you_think=( "a b" "c" "d" )
for sneaky in "${not_what_you_think[@]}"; do
echo "This is sneaky: ${sneaky}"
done
This is sneaky: a b
This is sneaky: c
This is sneaky: d
It could be an issue with the codecs (browsers are usually pretty limited in what they support). You could try to use a client like Jellyfin Media Player instead. It bundles libmpv, so it plays almost any video format there is.