Kozov,
I was unaware of the Rikanti’s usage of Targum Yonosan (a citation would be appreciated). However you are still missing the point. Why do we not find mention of a Targum Yonosan al HaTorah until the middle Rishonim? Why don’t we find it mentioned in the Bavli or the Yerushalmi or the early midrashim? Why are we using Onkelos and not Targum Yonosan?
(btw Even if Rashi is quoting from it, he never refers to it as Targum Yonosan)