We're 25/26 games into the season. Look at how many Arsenal and Liverpool's best centre backs have been involved in this season in all competitions (excluding the FA Cup for some reason).
Saliba - 34 game (2865 mins)
Gabriel - 35 (2825)
Van Dijk - 35 (3147)
Konate - 28 (2177)
Gomez - 17 (865)
Quansah - 17 (757)
And now compare that to ours:
Akanji - 30 (2357)
Dias - 23 (1673)
Stones - 19 (1091)
Ake - 19 (966)
Khusanov - 3 (234)
Simpson-Pusey - 5 (222)
Liverpool and Arsenal are clearly seeing the benefits of having a fairly settled CB partnership, and in particular, their best player being fit literally all the time. Meanwhile it's telling that for us, the CB who has played the most is the one that probably would be playing the least if everyone was fit.