Yes, there are no guarantees but you would imagine those 3 are going to peak some years from now, then be at that level for quite some time. Possibly Mendy too, but we haven't actually seen him yet ;) Not to any degree anyhow. Walker has several years left.
The great thing about that is, in those positions, once you get it right, you don't actually need 'freshening up' you just need more or less the same thing, over & over, forever. If we could nail it with two cbs & a keeper, we have that solid base to work round. Then it's a matter of replacing VK soon possibly with a young player & Otta in a few years time. We won't be in that position we had when Lescott went & we patched up then Zabba etc just got too old, because we have years to plan for it.
We can do all the changing players & 'freshening up' with the rest of the team.