First of all it is taking over again one more time. The second thing that I will point out is, no its not good if it going down as it will take the bitcoin's first position from the top coin list and if its dominance is going down then surely its because of the market cap for the same is dropping as well. So for your consideration if you are a bitcoin fan then I am sure we are not going to see the BTC dominance falling down.

And altcoin prices do not rely on the btc at all so you dont want to see it going rock bottom.