I think the most likely mainstream crypto adoption scenario is one where Bitcoin is adopted as a monetary standard and a number of centralized or decentralized payment methods are used to move BTC around to be settled in bulk on chain. That's because stability is key in international trade. Cryptocurrencies are borderless, which means that what keeps national currencies going, which is that they are legal tender by government fiat in one country, won't be a limiting factor in crypto adoption. The lightning network might eventually be one of the few decentralized payment networks able to scale sufficiently on a global scale. Many centralized networks already exist that could be used to transmit BTC off-chain at a sufficient scale.
STEEM is a utility coin whose value is entirely tied to the value of the Steem network. I don't think it will ever be adopted as a universal payment system. Despite its high maximum throughput, I would still struggle to scale, and most importantly, STEEM's monetary policy is unstable and has a history of being changed too easily for it to serve as the basis of a monetary policy superior to that of fiat.