Different situations are possible. But the situation you described is slightly more probable, the reason is simple: all the alts are traded against BTC, though priced in it and it takes some time to market to adopt.
as long as bitcoin has the highest exchange conversion volume of each exchange market, then they will remain a verbal reference for altcoins. even though ethereum or even Tether already has its own conversion, but many people still focus on bitcoin. This is because the bitcoin factor is still fluctuating positively where many people expect bitcoin to rally highest.