Yes, you will get an additional profit when trading the ETH/BTC pair if the market is in a bullish phase. But if you continue to trade this pair when the market changes to bearish, then your profit will be significantly reduced, and perhaps even reduced in dollar equivalent.
Of course, this applies to the negative scenario just as it does to the positive scenario. Although I only mentioned the positive scenario in my comment because the content is based on a positive scenario, a similar situation will also apply to the negative scenario. For this reason, it is always beneficial to choose the transaction parity to be preferred by taking into consideration the market conditions. In addition, it shouldn't be forgotten that in the event of a possible negative scenario if Bitcoin dominance becomes high and Bitcoin loses value there will be a loss both on Bitcoin basis and USD basis due to parity (like a double loss). Certainly, choosing transaction parity considering both scenarios will minimize possible risks.