A legal entity is required for many reasons, like getting on a top 50 exchange or to create legal obligations by the team to perform their duties. But the fact that the company is incorporated doesnt affect decentralization. Things that affect decentralization are: who controls the hash (GPUs vs ASICs), is there a private pre-sale to a small pool of investors (Zel had no presale/ICO), and what does the project actually do (Zel is creating a fully decentralized, trustless network of computing power via incentivized nodes that can be owned by anyone.