The first part of this is right--they won't trade Kamara. But Jeanty would see much more than 6-8 carries a game. Even before becoming the HC, Kellen talked about the value of the two-back system similar to what the Saints had with Ingram and Kamara. Jeanty would be the bellcow and Kamara would have a role similar to what we saw in 2017 and 2018.
The team will not take 3-4 years to rebuild. But aside from that, building a team requires a collective process. It necessitates drafting well (not just in the first round) and using free agency to shore up areas where depth and/or talent is needed.
I am oft-amazed when fans are against drafting a particular position such as RB in the first round on the premises that we have other needs or that we are rebuilding. In the case of the latter, you take good talent wherever you can get it. Jeanty is an elite talent and this team needs more blue chip players. In the case of the former, one round does not make a draft. So, even if the Saints draft Jeanty at #9 (and right now, based on what I've heard he would be strongly considered), they will still have other rounds to tackle needs at other positions.
The last thing I'll say is generally teams like to rebuild a team by focusing on the trenches. The Saints have done that more than any other team, using first round picks on the offensive and defensive lines. It hasn't panned out. Then you look at a team like the Eagles who has one starter on the O-line who was drafted in the first round and who has a mix of guys on the D-line drafted across multiple rounds and you see why it is important to see the draft as a whole and to add talent that aligns with your vision.
There are many teams that have fallen into this category. Finding a franchise QB, to be clear, isn't easy. Then again, there are teams that had messier situations and who quickly rebuilt. It is about hiring the right people and then building the team with a real vision for developing that team into a perennial winner.
Also, I wouldn't say the roster is awful though I know that tends to be a common belief. The roster is devoid of blue chip players but it isn't awful. Jeff and his guys have done a solid job adding talent. The biggest issue I see, aside from injuries, is the talent is not being fully developed/utilized correctly. Of course, we see this with Baun. But I even think about someone like Foskey who played the "vyper" role at ND (OLB). He rarely played his hand in the dirt and generally operated out of a 2-point stance. Yet, we brought him in to play in our even front. He is one of the guys who could benefit from the potential transition to a 3-4. I think about Cesar Ruiz. I have known and worked with Ruiz going back to his days at IMG. He is best suited to play center. He played some guard early on at Michigan because Jim started Patrick Kuglar at OC. He struggled at guard. But once he moved into the starting lineup at center, he dominated. Yet, because we have McCoy and given Ruiz's injury early on (that kind of derailed the move to center), he plays right guard for us where he has ups and downs. He is a very smart and talented football player but I think he is not playing at the position he is best-suited.
So, again, there's talent. The cup isn't bare. But there has to be better coaching and better vision for the players we bring on the team. We will see how Kellen and his staff develops the team.