I do not see why only those two altcoin are the only ones with legitimate aspirations to displace the bitcoin from its current leadership. In fact I do not even see in the near future that bitcoin can lose its hegemonic place as the most popular and coveted of all cryptos, although I have no doubt that eventually and by mere speculation some other coin could take in a temporary mod the first place in marketcap. In addition raiblocks is a very new altcoin that few really know, and there are still big projects to emerge throughout this year.