Bitcoin Ethereum and Iota consensus algorithm competition

Consensus algorithms can be changed in a blockchain platform. This makes me more confident about Ethereum because with Vitalik Buterin as leader I feel they are on top of this and can adopt a new consensus algorithm if its found to be the best. On the other hand, this concerns me long term for bitcoin which doesn't have a leader and struggles with upgrades. Will it be able to scale fast enough to maintain its lead? Iota is a coin I am researching because its consensus algorithm, Tangle, looks innovative and interesting. One of their founders created the first proof of stake algorithm in NXT. I am still researching this algorithm to see if its the next great thing but even if it is, I am not sure that is a threat to Ethereum as they could just adopt it. I am continuing my research and will keep you posted.