The key thing here to look at is potential vs their market value.
Skriniar has more market value today than De Vrij, Bastoni, or most of our squad. At the same time, his potential is lesser. Another season like the one he had, and his market value will plummet. And at the moment, is is looking like that.
I definitely feel D'Ambrosio is a better fit for RCB than Skriniar is. He adds a lot more to our game.
The Skriniar of 2 seasons ago was fierce as a lion, he had a great sense of when to tackle, wasn't intimidated by any forward. What we have today, is a pussy version of that. Not only does he gets beaten by many easily, but he loses far too many physical battles as well. His tendency to go down with the lightest of touches beats anyone else's in our squad, much worse than Lautaro.
Other fact is that he hasn't scored for 2 seasons now. And that threat is very important in a CB. He scored a lot in his first season, but that has gone away with the rest of his attributes.
For our 3-man defence today -
RCB - D'Ambsorio > Skriniar
CB - De Vrij > Skriniar
LCB - Bastoni > Skriniar
Sure all that could change in a 4-man defence, but we know that isn't happening for a while. And even if it does, a De Vrij-Bastoni partnership might be better than Skriniar partnering either of them. The others are better than him from a distribution and ball playing ability perspective, they are more of a goalscoring threat, and not comparable in other aspects of the game.
I have enjoyed Skriniar's (early) performances a lot, but his game hasn't developed since then. And this seems to me not a sacrifice to raise funds, but a practical call where the player may not reach the potential we believe he has. If he does, I'll be happy for him. But today it seems like he is heading down the Kovacic/Coutinho path where the potential remained that.