It's never promised cheap and fast. Something properly decentralised, though it may not really be that at present, can never hold a candle to a conventional centralised service. Others do promise cheap and fast but let's see them at full capacity for years before deciding whether that claim is true.
ETH failed in its current form at that when enough users arrived too. But it wasn't claiming that either.
Indeed!
Many those coins which promise fast transaction and less fees might fail when their adoption rate matches Bitcoin's. Lightening Network is in process of development and it might very well get implemented by next year. High fees and slow transactions are indeed the problems. But before that becomes a problem in growth of bitcoin, LN would be operational.