I agree with the general gist that slaad as presented make no sense. However, I would also assert that demons in D&D lore do a poor job of being CE, devils do a poor job of being LE, modrons do a poor job of being LN, and the others probably only avoid this observation simply because they've never been very much represented. Also true, Drow do a poor job in fiction and D&D lore of being CE, and Paladins do a poor job in fiction of being LG.
Part the First: Introduction I will now undertake to do something which I know to be foolish – provide for the reader a summary and overview of the race which is most commonly called ‘Slaad’ amongst the learned. There is much that is said regarding this race which is sheer poppycock and...www.enworld.org
There's some truth to this but I think there have always been takes on those other beings that work pretty well, and not all of those are meant to be supernatural planar exemplars. Drow aren't exemplars, for, um, example. I'd further point out that it's a common but I think illogical and slightly unreasonable take that because a race has a complex social order or societal systems it cannot be individually usually Chaotic. Not saying you're saying that but it's a common objection to the Drow and I feel a very weak one. Chaotic just, to me, may just mean they're not very keen on sticking to the rules, even as they might push the fiction of them when it advantages them. Still I do think NE would be a better average alignment based on lore, so I'm not entirely disagreeing!