I think that's a common misconception of Hive devs, in part because the current 2nd layer DeFi services on Hive (Hive-engine and DLease) are currently implemented as centralized services. I had this same argument with several of the devs here at BlockTrades, who felt the same way as you do.

I tried to briefly layout in this post how you can simply achieve decentralization of your 2nd-level app by opensourcing it, but I didn't go into depth on why this works.

Given the length and complexity of this post, I decided to leave those arguments to a separate post, so as to avoid cluttering the overall theme of this post. But just to be clear on my central thesis, I think smart contracts bring almost no benefit over 2nd layer apps in terms of decentralization (in fact, I think it's the other way around in terms of which is more decentralized). More to follow in that later post :-)