Saddle Bags are very light and efficient. come in many different sizes. why add extra weight....
I see what you mean and agree, but when you said saddlebags I thought you meant in the traditional sense, i.e., panniers. Your pic clarified. For my needs, a structured box trunk bag offers me much faster access to the myriad things I have in it, versus unclipping and unrolling an XL seat bag. But no question, bikepacking gear is lighter.