A couple years ago, I was a Bitcoin Maximalist. In those years, it's been made plain that Bitcoin's development teams and major stakeholders lack the leadership and ambitious roadmap necessary to take advantage of their network effect and mindshare penetration advantage. They're not going to solve bitcoin's problems and plug in needful functionality fast enough to stave off Ethereum.
At the time of this writing, BTC's price is below $10,000, down over 6% in 24 hours. Meanwhile, ETH is up 1%, at over 2/3 of BTC's market capitalization. This is all while bitcoin continues to be synonymous with "blockchain" by the mainstream media, normies, and most of the financial class. The stunning thing about ETH's advance is that it's been despite ETH not enjoying a hype cycle similar to what Bitcoin and Ripple enjoyed. Ethereum has crept up on Bitcoin like a ninja, coming within striking distance of The Flippening while only experiencing 15% of the hype.
Believing that a flippening isn't imminent requires believing that none of the code Vitalik plans to bring online in the coming months will actually come online. It requires believing that none of the thousands of ambitious smart contract projects being developed on Ethereum's platform will succeed. It requires believing that ETH's growth won't produce a "bitcoin's dethroned" media hype cycle which will finally deliver the one thing ETH hasn't enjoyed yet: stupid money.
Several ambitious and well-funded projects claim they're closing in on smart contract platforms superior to Solidity. Even if they're all as smart as they say they are, they don't have Ethereum's head start in terms of cultivating a large community of experienced developers. Insisting that they won't experience any of the setbacks and growing pains that Solidity experienced strains credulity. By the time they manage to catch up to where Solidity is right now, Solidity will be even further along.
Almost all of the altcoins either propose solutions which would be more gracefully and sensibly implemented atop Ethereum's VM. Excluding them, you have the privacy coins, which Ethereum promises to deliver a solution for, and you have the microtransaction currencies like IOTA and NANO (formerly RaiBlocks). Further innovation in cryptocurrency will almost entirely take place within Ethereum, either as innovation atop its VM or as forks of Ethereum's codebase and blockchain.
At the conclusion of "The Last Lecture," a famous speech by a young and charismatic professor who had been diagnosed with pancreatic cancer, he offers his daughter (who's a toddler at the time) some timeless advice: ignore what the boys promise and say, ...listen to what they've actually done. Several of the coins and tokens make tremendous promises, but none have managed to deliver with the rate and reliability of Vitalik's team.