I've heard multiple times that this dominance calculated by the share of the total marketcap is not saying anything. In a sense, it is true because there are coins with a huge supply and a regulated price which makes their capitalization big or even coins that are worthless but the supply is so big that they still make a difference for these figures. Moreover, this 'record low' is so high compared to Bitcoin dominance (or the lack thereof) in 2017 that it should not be taken seriously as a sing that the alts will have their comeback. The situation still looks great for Bitcoin and pretty bad for the bast majority of altcoins, and I don't think that even the strongest are currently being serious competitors for Bitcoin.