Baseball is an individual team sport. Thinking "clubhouse presence" is somehow significant enough to extend an aging, bad defensive player is goofy. Giving Abreu a guarenteed roster spot 3 years from now is not a good baseball move, regardless of how much you like him.
Vaughn is in his first month + of professional baseball and they just spent the 3rd overall pick on him. Unless he turns into trash you can probably expect to see him in 2021 or very early 2022 based on what the Sox have been doing. There is 0 reason to guarentee Abreu a spot for 2022.