I have Jupiter R in Leo the 11th house, I am not a big socializer only on Astrology Forums. Maybe this just represents the inward expression of this planet. I have heard with Retrograde planets you are still learning to master these energies inwardly, before you can confidently express them outwardly. Strangely enough since this Mercury R we are having I have been a lot more inward thinking than I usually am. I have been reading my Astrology books, and wanting to be alone as I internalise all the information. I haven't noticed myself being like this during other Retrogrades, possibly because Mercury has been going through Pisces this time, I have a dominant Pisces chart and Mercury is my Chart ruler. Maybe this explains it, but I have definately been different during this mercury R.
I imagine a Retrograde Jupiter works in a similar way maybe internalising the Jupiter qualities of hope, faith, optimism, internalising what you beleive in, maybe lots of internal self growth and understanding, and once you have fully internalised all these qualites into your self, in your case with the Jupiter R in the 1st house you will outwardly in later years project all the internal wisdom and understanding and all that you have learned, and other people will pick up on the faith you have in your self and the optimism you project. In my case with Jupiter R in the 11th, I may be more expansive in groups, and learn a lot through groups which help my self (Leo) expansion. A bit like my interaction on here, where I learn with and interact with other people from all over the world, and I learn how truly alike we all are and we all have fears, and worries and problems in our life no matter who we are or where we come from, so I have experienced a lot of growth and learning from people on this site.
I personally wouldn't class Jupiter R as weak, it is very strong in internal expression. You are learning to understand your beliefs from deep within to have an inner optimism inside, and broadan your self knowledge, and once you have fully internalised the meaning of what this planet is teaching you, you will be ready to truly express this planet outward as a fully internalised part of yourself.
P.S Just theories, to work with. You know your own life and how your Jupiter is expressing itself.