Support... the development of theorycrafting and min-maxing was inevitable with the increased popularity. The only design decision they could make for this to not be a thing would have been to keep all raids at MC-difficulty level. Which is to say "raid is easy enough that we can take almost anyone since we won't really fill it with 40 decent people anyway".
Since people started getting better and playing smarter and realizing some classes do better than others, all you could do design-wise was increase the difficulty, make it tighter, make more complex mechanics. Because of these changes - playing randomly whatever you wanted just wouldn't cut it. And because of this, reading up on how to get better became a thing. And it became a thing pretty early too, it's been over a decade, this isn't a "nowadays issue".
The only more recent thing, maybe since MoP (which is still like 6 years old), is logs becoming increasingly popular as "global dps meters" and raid leaders misusing them to judge performance and even award loot. But that's not really a design thing, it's people's fault for being limited and not understanding "context".