Bitcoin's dominance would be probably close to 100% if we were to exclude all the useless shitcoins and tokens from these crypto rankings lists. I'm personally not concerned at all about the % calculated anywhere - whatever happens, we all know BTC is almost always needed in the end.
Right, shitcoin is shitcoin anyways, and one of the problem with these supposedly altcoin that has balloon their marketcap like XRP is that it can affect bitcoin dominance. But no one care, at the end it will still be bitcoin that will remain on the top of the food chain.
Well as new altcoins starts to flourish the dominance of bitcoin will decrease. As long as it continues, dominance on the other hand will decrease but that doesn't matter. What matters is that we all know that bitcoin will continue to increase and it is still the main asset to be held.