Are you referring to miners? They are neither undetectable, nor exceptionally powerful. They do have an environmental impact, but the bitcoin community believes the juice is worth the squeeze.
I don't know why this is getting downvoted. The current assumption that colluding miners are detectable is absolutely false. There is no way of knowing whether a block comes from a specific mining farm/network as all information about that is forgable by the creator of the block.
If you try to mitigate this by controlling who has access, you just eliminated the advantage of being trustless and thus made blockchain an expensive database.