Not sure i agree with this.
Milan are obviously a tough one because they lose players on a free and they mostly replace them rather than truly reinforcing the team so any opinion would be subjective. But for me their balance is positive. They lost Donnarumma and Hakan on a free but they spent 80m on Tomori's redemption, Maignan, Tonali, Giroud, Florenzi, Messias and some young prospects they signed. Maignan isn't as talented as Donnarumma but he's a good GK. Tonali was excellent business and their season revelation, along with Kalulu. Giroud was crucial in their Scudetto while Mandzukic had offered absolutely nothing. We don't know what new owners plan to do but under Elliott the plan was replacing Kessie with Renato Sanches and Romagnoli with Botman. This doesn't look bad at all in my eyes.
Juve may have lost Ronaldo last summer and Dybala this summer but they have spent 180m since last summer and they'll probably spend even more this one. They're already close to Pogba and Di Maria and they're linked with Kostic, Raspadori, Jorginho, Muriel and Udogie who are all tied with contracts. They underperformed last season but in terms of squad quality they have really improved.
On the other hand, Inter have lost competitive advantage they had after Scudetto. They lost Hakimi and Lukaku and replaced them with lesser players (also lost the coach but i don't want to turn this into Conte vs Inzaghi) and the trend will probably be similar with more core players this summer. When ownership demands substantial profit from mercato every summer then this can only lead to club's downsizing. Even the best management could only slow down the process.