Bitcoin is an internet protocol, Ethereum is an internet protocol. Protocols are very sticky. They don't get replace just because something is a bit better. As Peter Thiel says anything new needs to be at least 10x better to stand a chance of competing. read "HOW TO POSITION FOR THE RALLY IN BITCOIN" by Tuur Demeester https://casebitcoin.com/docs/HowToPositionForTheRallyInBitcoin_TuurDemeester.pdf1
side note: It is even questionable whether something can be better than BTC or ETH. What most protocols do is they just choose different set of engineering trade-offs, i.e. they are worse at something and better at something. e.g. Monero has privacy but it has 10x bigger transactions than bitcoin and it has directly un-auditable monetary supply so a risk of an inflation bug.