Philosopher, the minute you move the Bar Mitzvah away from a shul setting, you are saying “This is not only about the mitzvah.” The symbol of Bar Mitzvah is laining, something that happens in a shul setting.
A wedding can be anywhere – there is no typical location for a wedding (at least, of real significance). So you need a location. And you need a seudah. And you need to be sameach chatan vkallah. Plenty of good reasons to have it in a hall where your family and friends can join you in this mitzvah. Please tell me how that compares to a Bar Mitzvah.
If you want to play the tznius aspect, then any event which focuses on women (including graduations) would be banned.
And you can’t control your daughters feelings. You may try to raise them a certain way and they may be jealous anyway. I didn’t grow up with brothers, so it didn’t really affect me.