i know that by default zsh is not 100% bash compatible but... i say this even as someone who likes 1-indexed arrays better... i can't imagine maintaining the level of direct bash compatibility they have while also making such a weirdly huge and ultimately unimportant change
regardless, i still only use bash for my shell scripts just for portability sake... maybe one day i'll care enough to change that, but eh
remember, if you're testing shell behavior for a bash script, make sure to actually launch bash rather than assuming zsh behaves the same way