Ethereum can never come first. Where will you place bitcoin should ethereum comes first. This is not even possible. Remember that ethereum bullish with bitcoin. So it virtually wrong to say ethereum would come first.
Ethereum is technologically much more advanced when compared to Bitcoin. But as we have seen during the past 4-5 years, that factor alone is not enough to make Ethereum the no.1 cryptocurrency in terms of user-base and market capitalization. Also, one of the major applications of ETH was in the ICO market. But that sector is not in good health right now.