I use Nix every day. I love it, but I'd be lying if I claimed it things less complex. I don't think that is very controversial. To build software using Nix you still need to understand how that software builds without Nix plus you need to know some amount of Nix. If the abstraction was airtight, then I'd agree, but currently, it is a very leaky abstraction. But that doesn't mean it's bad, just a trade-off to consider.