The motor controller mediates power delivery from the battery to the motor completely. Motors should not inherently be able to break a battery. Something about how that battery module was operated or exposed to the environment would more likely be the issue.
I have plenty of criticisms for Zero, especially regarding their owners manual, and they should provide more material justification for their decision, including pointing out what evidence (logs, etc) they used.
But it very much sounds from your first post like you beat both of your bikes destructively, and need to learn to appreciate the limits of the vehicles you're given. If you ride a machine to its limits consistently, it will break.
The FX in no way that I've ever noticed is marketed as some kind of KTM equivalent. KTM has its own reputation, and KTM bikes do break. Marketing is an impression, anyway, not some kind of hard claim.