I do think the midfield will hold for this season, Santos is essentially replacing Casemiro, and Tielemans is a quality addition for extra competitions. We'll have more Mainoo, and possibly a little more Mount. We spent very little and managed a tricky situation quite well.
But we needed strengthening in other areas too, and while we may just scrape by into CL next season, unless we don't make quality moves now, we're in trouble for the next window.
We'll quickly need a new starting LB; more CBS to replace the injury-prone and aging trio of Maguire, De Ligt, and Martinez; a Bruno replacement; a direct, beats-his-man left winger; and a capable second striker. All of this just to stay in the CL the next season, not compete for top honors.
The good news is - despite what it may seem like - our rivals are not improving as much as well. Arsenal are only getting Guimares (hopefully no Vini). Liverpool have a new manager but haven't replaced Salah, and are a top heavy side with a crisis in defense. City have lost their magic with Pep gone and are replacing Rodri/Silva with Anderson alone (they already preplanned their business with Cherki and Semenyo). Villa have just replaced Rogers and Tielemans with Manzambi and Homes.
The only sides to have actually moved forward a lot are Spurs and Chelsea. Both of whom have new untested managers and were starting with poorer squads than ours. That being said, they've really moved forward.
Chelsea look good for a CL run - Quenda, Rogers, Lacroix, Pelestra, Barco in and only Santos, Cucurella out, plus Alonso is a much much better coach than Rosenior.
Spurs - the story of the summer - have a fantastic manager in De Zerbi, and may have just bought themselves a CL place with good players returning from injury and additions in Fernandes, Tonali, Van Hecke, Senesi, and possibly Gakpo. Incredible window, and the cost of it will soon be forgotten for the returns it generates.
As things stand - two of us, Liverpool, Villa, Chelsea, and Spurs are going to lose out on CL next year, and it's gets more difficult the summer after. Let's hope Carrick can keep delivering his magic.