Agreed.
First choice is just not that relevant anymore as a concept. Who is first choice in City's defense? The whole point is that they have 6-7 high quality and versatile players competing for those positions, they can change based on matchup, and they can withstand injuries without having to change their style.
The important thing for any team trying to play a similar way - which we certainly are - is to also amass 6-7 defenders that can play a possession-dominant game while also having the overall athleticism and strength in duels in the group that is necessary to defend a high line. We've got five for sure now (Saliba, Gabriel, White, Zinchenko, Timber) with another two guys that have the potential to be good enough (Tomiyasu if he can stay fit really, Kiwior still a bit raw but he has the athletic and on-ball tools).
I personally still think Tierney will go this summer. I just don't think the role we can offer him (essentially, if Zincheno isn't playing he'll be able to compete with Kiwior for the LB position) will be enough to satisfy him.