If we check history, when Bitcoin crashed from $1,000 to $200, bitcoin only pumped back to $1000 when their dominance got pumped as well. and then, finally the whales dumped their bitcoin for altcoins for few months. And, during the bull market 2017, once again bitcoin dominance got pumped all the way until November 2017. alt season only lasted in less than 2 months before market crashed. Thereby in my humble opinion, the dominance percentage doesn't really matter here. people dump bitcoin for altcoins when they already gain good enough ROI and vice versa.
With the huge volatility of bitcoin there, the dominance would not matter if there will be a crashing news that awaits bitcoin in the future. Same goes regarding a huge hype, prices could change too fast and as a result, the long term market dominance of bitcoin could easily fall down with altcoins replacing the rank one. Though, people especially us will not let this to happen that is why we still believe and hodl bitcoin.