At the rate coins get created, I won’t be surprised to see bitcoin "dominance" go lower than 50%. It's very normal because people will use altcoins to get quick money, and that is why these coins always dump because people sell off to get profit at every chance they get.
As for me, I willwill be surprised to see Bitcoin dominance get to that 50% because I don't think it will, irrespective of how new altcoin are being created every day, you already defined what people are using it for, to get quick money and that tells you that they can not hold it for long like Bitcoin and at the end of the day, Bitcoin will still remain dominant up at 70% and not less than that. I don't think that any smart Bitcoin investor of this era will sell their Bitcoin to far altcoins.