Midfield and defence are their problem areas as you identified. Well that and just odd investments such as Bergwyn, they were crying out for a backup striker when they brought in Bergwyn. In fact Bergwyn ended up playing a game or two as striker because they literally had no one else. Then they bring in Bale for that same position, so now you have Lamela, Moura, Son, Bale and Bergwyn, how many wingers do Spurs need? I guess Bale will be going back to RM so there is that, at least now they have a backup to Kane in Vinicius.
Midfield and defence, average to bad. Hojbjerg has been good tbf, do not rate him as highly as Ndidi but he is the anchor for Spurs midfield. And as you mention they have some world class players up top in Son and Kane, although come the end of the season and no CL or trophies. Will see if either remain at Spurs. The midfield has been in decline since Modric left really, they had Dembele who in his own right was a gifted midfielder, but even he wasnt a patch on Modric. Now you have Ndombele, Sissoko, and Winks, none of whom are in the class of Dembele in his prime, let alone Modric.
The defence is an aging Alderweireld, who is probably the best CB they have, a converted DM in Dier and Davinson Sanchez, both Dier and Sanchez drift between ok to bad. I certainly cant say Ive seen a Spurs game recently where the defence has been impenetrable. There were times with Vertonghen and Alderweireld in their prime I thought Spurs had the best defensive duo in the league. Outside that you have an academy player in Tanganga and a young Welsh lad who is finding his feet in a new league and trying to make the step up in Rodon. I guess Davies can play on the left in a back three if required.
Aurier has improved tbf, was a walking red card at one point, still question his defending, the Doherty acquisition I just dont understand, they should have gone all out for Aarons when Norwich got relegated. Reguillon is really good, but a loan so it is w/e, Davies is ok if uninspiring, solid LB, provides little going forward.