This "lightness" of HoloChain sounds good, but what about 50% attacks and double-spending? As you wrote, Holo nodes are "light", they need less computing capacity than blockchain. It is a good thing, but because of this, a possible attacker can easily start 1000s of nodes to commit a 50% attack. PoW needs much computing capacity which is bad from one side, but from another side, it protects the chain. So, HoloChain's "lightness" is a good thing, but it also can be a possible security problem.