They have played the market well.
Their main weaknesses were CB and GK. They have got an experienced, quality CB for free. There's only a certain amount of names that would be a better option than him, and some of them cost £80m like Koulibaly which would've wiped out a significant part of their budget. If Silva is good for a year then it will be an excellent signing, plus he will bring experience and leadership to the team. Sarr is another free transfer at the start of his career, give him a year on loan and phase him in next year if he does well. Makes it a last chance saloon for the likes of Zouma, Tomori and Christensen this season.
They'll get a GK in the next few weeks I'd imagine. The guy at Lille or Onana if they can convince Ajax to sell at the right price.
When players like Ziyech and Werner come on the market at reasonable prices, you've to try and get them which Chelsea have done. Same with Havertz who could be one of the best players in the league in a few seasons. For the money spent on the attacking players, they've potentially set themselves up for years. Spending that sort of money on CB's and GK instead wouldn't have set them up and they may have needed replacing in a few years or without the same guarantee of success. In addition, it would've caused problems at the top end of the pitch as last seasons options aren't really good enough for their long-term ambitions.