Market dominance is based of the market cap of the currency, and imo, that is not a very meaningful statistic, does not reflect growth, and I will not pay much attention to it. Any altcoin created today could easily pump up their volume and release unlimited number of coins, greatly increasing their market cap. When checking Bitcoin, I usually pay more attention to other metrics.

2017 into 2018 was the hype period for ICOs, the current rave is DeFi, there will be more hype projects in the future as more developers look for ways to tweak the system for benefits. This doesn't much hurt Bitcoin as a network, those that understands its value will get in and those who follow the hype of other projects could profit there or get burned just like with ICOs back then.