It's funny because we have the best defence in the Prem currently, but if you listen to what people say here Toby is washed, Dier is not a CB, and Sanchez is a clown. I think Toby has been excellent personally, outside of the Everton game.
We've yet to play against a free attacking side though, City was a test sure, but they've failed to score all season, so the "test" of previous seasons it 100% wasn't, they aren't scoring this season.
Dier has been the player that's been "on his toes" since he regained his fitness, so for me, this pre-dates this season.
People looking to pile into him because of a now ridiculous law on pens (handball), with players also falling over in order to win them (they don't get pens for fouls if they stay on their feet so who can blame them) but it boils down to this DON'T go using a defender conceding a pen as a reason to have a pop, they can't win. Look at everything else, look at their positioning, look at their 1v1 duels, look at the player next to them for the context of how a partnership is working or not.
Every player has flaws and with CB's imparticular those flaws can be equalled out if their partner can cover the flaw. We've enjoyed this with Jan and Toby for years e.g Jan the better baller, bring the ball out of defence with the ball at his feet drawing oppo onto him creating space in midfield. Toby on the other hand was the one to ping diags out to pushed up FB's. Toby used to be one of the best 1v1 defenders in the game, whereas this was Jan's biggest weakness.
Saturday's game aside Toby has been a shadow of his former self, unable to defend 1v1 and his diags once so accurate have been hit or miss. So, his strengths have been no longer his strengths whilst his weakness remained, slow on the turn, can get caught with the ball at his feet especially if pressed, the limited pace has now become no pace (Giroud out sprinting him!).
Does he have the partner to cover his weaknesses? No - Jan could no longer (wipes tear from cheek). Sanchez can cover his pace but needs to play on the right (Toby's position), doing so means we lose Toby's now less reliable (but still good) diags if played on left, ergo less on filed solutions. Dier getting up to speed as CB ALSO having to adjust to LCB (not natural to him). Rodon is an unknown to me and obviously has played yet.
Is Toby finished no of course not, he's still a good defender but he's been miles off from where he was as a consequence it's been Dier that has been the player covering all of his deficiencies whilst still adapting his game to a) being a CB b) playing on the left.
When we play propper low-block, as we did Sat, then he adds major value as his weakness aren't exposed (all defenders should find it easier, it's how Newcastle & Palace stay in games if they can do it, we've a problem if our boys can't). When we play against a side that sits deep then Toby can (has been) an issue at the back, especially as his pace has gone the ball behind him is always on, players running at him (used to be his strength) leaving his feet in knots.