Which year of their career did Hassan Whiteside, Rudy Gobert, Steven Adams become consistent studs? Nurk is in his 4th year and didn't play a ton of consistent minutes before coming over last year. How old was Marc Gasol as a rookie? 24? Nurk's 23.
Tell you what...here's all the centers on rookie contracts (or just off of them) in the league right now. Tell me which one or two you'd rather have/pay for the next 4 years entering their prime than Nurk (non Top-5 pick category)...
Bender, Porltl, Sabonis, Papagiannis, Maker, Zizic, Labissiere, Cauley-Stein, Kaminsky, Myles Turner, Hernangomez, Capela, Len, Noel, Olynyk, Nogiuera, Plumlee, DIeng
Aside from top 5 picks (Davis, Embiid, KAT, Porzingis, Boogie), which we famously haven't had since LMA/Oden, we've struck on one of the best centers of the generation. And we can keep him if we want.
And even if we did let him go (let's even go so far as to assume we get a 1st-round pick somewhere between 6 and 26 for him), the chances that we find a consistent, two-way, legit-7' center entering his prime as productive as Nurkic already is in the draft is very slim.
I'm ok with paying him. I'm ok with paying him a bit of a premium.