Bitcoin always dominance how ever price because investor have higher trusted with bitcoin than altcoin, Bitcoin have stable price every day when bitcoin down just take few weeks for get back to higher, for altcoin less dominance because investor do not brave for holding altcoin in long time because after altcoin down never get back to the higher.
I don't even see bitcoin loosing dominance at any time for now and even when it reaches its highest peak where there is no longer volatility; it would still not loose dominance because that time is when people would rely more on using it for payment and accepting it also as payment because of its stability then.
The dominance of bitcoin does not even stop altcoins from performing, so we need to stop attaching the misfortune of some of these coins to bitcoin, they all have their own different use case, same as bitcoin has also. If altcoins really wants to gain dominance, they need to just act on their own real use case first and make sure they do everything possible to just attract very great investors or users to them, and then sustain them with their real use case.