It would be the exact same point as having James Young or Terry Rozier. You find excellent young talent, and give it time to develop. Eventually somebody gets hurt or he surpasses someone. It's entirely possible next year D Lee is outta here and so is Amir and so is Sully, and maybe even KO. Or one of them gets hurt real bad. You gotta look ahead more than half a year.
The Patriots once had the same problem with whether or not to keep yet a 4th QB on their roster. 4th QBs don't have a great track record in the NFL, and you never need one. Saw the talent. Kept him anyway. It worked out fine.
When you said excellent young talent I had to pause.. that is never going to be Bennett. Not his fault he was picked number 1 but he was never going to be a top player in that draft. And that was a weak draft too.
Although I get your point that next year our bigs lineup will be different. But I disagree on one front. They will be gone if they are packaged for a big name, otherwise Johnson will be kept as a large expiring, KO will be on his rookie contract an extra year and Danny will 100% not let Sully walk whilst getting nothing in return. Same with Zeller. So it's not like we'll suddenly have a torn down roster.
Bennett's "successful" summer with the Canadian national team was in a role as an effort rebounder. It's not like he's flashing solid dribble moves or showing of any kind of hook shot or post move. At least the other young prospects can point to something as evidence of a potential elite skill:
Rozier - Athleticism
Young - 3 point shooting (although I admit this can be highly debated)
Jones - Scoring and defensive versatility
Disclaimer: I said potential, I'm not saying they are elite in those skills, just that they could get there with the right mentality and coaching.
Basically I guess that's a long winded way of saying I don't think Bennett will ever be a star but our current young prospects might.