Thing is, the Holiday brothers are probably closer than most groups of brothers. They at least all made the NBA (despite different bodies). IMO, I don't think Jalen is any more relevant than another player's brother who you've never heard of, which is most of their brothers.
I think the frame matters because he's not just skinny, he's an unprecedented kind of skinny. Like he needs 15 lbs and then he will be skinny. There's no doubt he can add size, but he's 15 lbs from being 15 lbs away. As far as shooting, I agree it will make him a good NBA player regardless. Only concern with that is there really isn't a track record of him being a good shooter. His college sample size was so small his % is basically irrelevant, though the low volume is not a good indicator.
I have an opposite kind of feeling about him. I don't find him to be very toolsy. I guess it depends on what you mean by toolsy, but usually I associate that with guys with much better physical profiles and/or unique skill combinations. Tbh, I don't even know if I use that term right but Cody is not what comes to mind with toolsy. Things that you would typically associate with high potential. Like you, I think he can be a solid rotation wing and I actually feel good about him reaching that level....but it's hard for me to see much beyond that. If he does become a top 15 type player at his position, it will be as a super utility guy. Those guys are valuable.