That is a really good point to ask and even if not 90% and Bitcoin has 70% dominance like Coinmarketcap says
What I saw is people nearly forgot to look at the growth of both bitcoin and altcoins in their dailly liquidity. Liquidity growths give us very strong signal for growth of crypto currency market, in general. When demands increase, price will increase later, certainly. No one can answer when bitcoin will stop its domination in crypto market, like it has been so far this year. No one can answer when altcoins will officially start its season this year, or whether altcoins have their season this year or not.
Like what we all witnessed when bitcoin fell to around $3100 in late days of 2018, but bitcoin has never ended as dead one. It rallied, and brought happiness to most of us, especially investors whom bought at bottom range.
Believe me, altcoins will certainly do bring happiness to loyal, patient investors, whom hold them till the bearish period of altcoins goes away.
Important to remind altcoin investors that what I said only apply for good altcoins, for shit, scam altcoins, yeah, investors should take advantage of any pumps from news to get out, and reduce their losses.