To defeat Bitcoin, an altcoin would require not just superior technology, but such vastly superior technology as to be an advance over Bitcoin comparable to the advance Bitcoin represents over fiat currency. Furthermore, a truly great innovation would much better serve people by being incorporated into future versions of Bitcoin rather than by requiring them to switch to something else
This, even if a new coin was developed that was so much better than bitcoin if it is still based on the blockchain what it is going to stop the developers of bitcoin to adopt the idea? For example many wanted the bitcoin developers to add full anonymity to bitcoin but that will make the problem of scaling of bitcoin even more difficult so that has been left out and that is why anonymity coins are thriving in the market, but if that was not the case then anonymity coins will not exist and all their market share will belong to bitcoin.