The issue is timing. Grant is up a year before Sabonis. Monte would be walking a super thin line if he trades 2 FRP for Grant, keeps him on the big extension and Sabonis doesn't have a deal the season before his UFA.
Again, I think PJ is literally the same thing and honestly might be just as impactful already. While keeping all your future draft capital. I think the Kings need to play it smart and not quite push all their chips in yet on a season they're so far behind in. That can easily happen during the draft/FA/trade season and you come out the gates firing with a fresh record.