“we are criticizing their motivations.”
This assumes you know their motivations. Had the OP made no mention of Rabbi Weiss, would you have assumed something “sinister” about a simchat bat? I would have assumed the person was sefardi. It is a common custom, and is found in their siddurim. Does the OP know that the person who made the simchat bat is not sefardi? Conversely, I know members of his congregation who have not made a simchat bat for any of their daughters. I think the OP took a leap of faith and everyone has run with it. This does not mean that there are not feminists about who have created a ritual and coopted the name simchat bat for their ceremony, however, your statement that you know the motivation of those who make a simchat bat and that you take issue with that motivation is difficult to take seriously.