Bitcoin is still the leading Cryptocurrency as I do not see it's replacement for now. The most important Cryptocurrency for now is bitcoin and it will remain so for unforeseeable future. Many altcoin like ethereum are promising but bitcoin will lead Cryptocurrency!
The dominance of bitcoin that is too strong certainly makes the market not good, see when dominating no more than 35% then the market is better because investors still hope for other coins, but when the bitcoin marketcap reaches more than 50%, the market continues to drop like now.