Since unlike you, who tends to just ignore the question he's been asked, I tend to answer them.
As things stand, Toby is probably better than any of our CB's.
But that doesn't really mean he would have been an instant success considering that is I've mentioned before he failed in the system much similar to our at that time in Atletico under Simeone, besides I actually believe it's the Spurs system that makes him better than he really is.
Again, our defence is nothing like Atletico's. In fact very few defenses are e.g. there is no ball playing CB, they play as 4-4 defensive unit (back line tied to defense not lone DM), level of aggression in tackling, less aerial threat in la liga etc So stop using it as a measure against Toby. Also the quality of Atletico's backline is much higher and difficult to break into. The spurs system is actually more similar to ours: one physical+ one ball playing CB, +lone DM.
While there is no absolute certainty that Toby would make us better, but its almost as certain as you can get with a transfer e.g. matured player, played in PL and CL,for one of the top 6 clubs, no language barrier etc. Anybody else that is younger, coming from outside the PL, doesnt speak english, and/or from a lesser club would have more uncertainty about succeeding.
Now bear in mind, majority of people would tell you that Sanchez was also deemed better than any attacking player we had prior to him joining, and we know how that turned out...tho according to you he improved us
We swapped Sanchez for Mkhi and had a better squad after the transfer. The failure to reap full benefit were due to it being a mid-season transfer and mainly how Mourinho handled his integration (i.e. would things have been different if he was introduced on the right and Martial kept his place). While we dont have full details into what influenced Mourinho's decision, but there is a legitimate question to be asked but that does not change that Sanchez made us better. Was he worth the astronomical wages and contract - absolutely no imo
Then also Matić was deemed better than any DMF we had at that time, and he was for couple of months.
The longevity and value of the player is a different argument, which is why i am usually against signing older players unless for free (Zlatan) or on the cheap.
But in getting an experienced CB, I dont see how we can avoid it and Alderweireld would seem the best value. If the rumored numbers are true, then I agree with waiting till the summer to get him, but that should not have barred us from then getting another young CB, LB/RB or DM to stregthen the defence. The drop in quality of matic is a significant contributor to our defensive woes.
You're line of thought is fueled with assumptions based on Toby being the better player, but my thoughts are fueled by actual facts with actual examples of better player than we have actually flopping.
Also not to mention Toby would have been under additional pressure since we're a team that's happy to sit deep and soak the pressure which in turn makes us more prone to making mistakes.
It is not an assumption that Toby is currently the better player. i dont think it should even be a question.
That he is the better player is the premise of the transfer (otherwise why buy him) and his success after transfer would not have been any more uncertain than any other target. We can spend 200m on a player and there would still be uncertainty about his succeeding at the club, and maybe more so with the pressure of a very high transfer fee. But we cannot use that uncertainty as an excuse cos then we wont sign anyone of worth.