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.
Yes, but don't forget there are so many shitcoins got delisted and become deadcoins, it will increase the dominance of bitcoin. The dominance of bitcoin is very various on each site, in CMC 62,4%, Coingecko 61,2%, in bitcoindominance 78,58% etc. That's not the main concern which site is right or not because they have own rules to calculate and listing altcoins.