Lol ... Dier, mainly in the back 3, was part of the best defence in the Prem last season - and mainly as DM part of the joint best defence the season before that.
Moreover he's young, an England regular now and sitting on a long contract. Pochettino values him highly and Levy would laugh in your face at your valuation.
So go ahead and bid mega-bucks for whatever 'inho' player from abroad takes your fancy. Meanwhile Spurs will sit content with perhaps the league's most versatile player (yes, he's also done well at RB when called upon to play there).
I agree maybe Dier's a bit too underrated on here. As I recall he was considered quite a phenom coming out of Sporting, and rumours abound that United were tracking him then, and may have been involved in bidding. It's also very possible a certain Portuguese manager has had an eye on his career, as well, over time.
There are some things to consider:
1) He's a childhood United fan
2) Apparently his childhood hero was Roy Keane
3) According to media he's not being played in his preferred position at Spurs
4) He could presumably get a large pay raise
5) His name keeps cropping up in the media connected to United
Spurs certainly don't need to sell, and they don't have to. However, all of the above could potentially foment into an unhappy player who wants out. Unlike Kane, for whom none of the above is applicable, there is a potential with Dier that things could boil over into a showdown between an agent, an unhappy player, Pochettino having to manage that, and Levy having to hold firm with a player demanding out.
I'm not saying for a second that anything of the sort is actually happening, or will happen.
I'm not certainly not saying he's the right player for United, but I rate him more than others, and am certainly not going to judge him based on one poor appearance for an England team that is far from settled.
What I am saying though, is there are potentially factors there that could lead to a conflict between Dier and Spurs.