How will signing a guy past 2 years hinder keeping the core? Odo will be gone, Cruz will be gone. Rosario will likely be gone, if not in 21, then in 22. Of the core, only Buxton, Sano, and Berrios will need signing in the next two-three years (you aren't extending a catcher that can't be a free agent until he's 31 any time soon).