Depends on what you mean undid? Evra is old so after being quality placeholder for the left flank until Sandro came. Similar sitaution with Tevez being replaced by Dybala. Our defence is ageing specifically with 35 year old Barzagli, and he gets a younger equal level player in Benatia. Yes he is 29, but solving the ageing problem doesnt mean just getting Rugani level youngsters (who is there directly to replace Chiellini in long term), but also gradually addressing the problem, and getting 29 year old for that position is fine and not too old, nearly 6 years younger. Only way we lost our WC level youngsters are Morata and Pogba, and former is completely out of our hands, and latter wanted to leave and did for a record sum. Former is replaced by 5 years older player, not ideal for rejuvenation, but said player is considerably more deadly then Morata so its certaintly fine. Pogba is a big loss both in quality and youth, but ageing wise Pjanic isnt old, only 3 years older.
Now what we need to remember is the goal of the club, CL, which means we dont necessarily need to be thinking long term goals right now but immediate one. And secondly, why do you assume we are thinking short term? If anything, Marotta is showing he is very willing to pounce and make major changes in the squad quickly. Meaning just because we arent signing young studs this summer, doesnt mean we wont soon again, he is the same guy who signed Pogba, Morata, Rugani, Sandro, Coman, Lemina, Pjaca and Dybala as soon as opportunities for them were there.
Its all about timing and opportunities available, and how your fincances look at the time. We waited a little more for long term solution for LB by getting Evra first, that did not mean he didnt have Sandro in mind when he did, only that no market opportunity for it or something else is prioritized that specific summer but he had his eye on that ball for long term anyways. He pretty much has that for all positions, we wouldnt be in this high level state of our team and squad if he didnt. So us signing Dani Alves, ONLY OLD PLAYER WE SIGNED THIS SUMMER, look at it as another Evra sitaution IMO (except MUCH BETTER

), and think what kind of quality younger RB are we looking at? I hope its Bruno Peres more so then DSC...
The rest? 28-29 year olds arent too old, they will have plenty of years to service us in top level if they are good enough. And when the opportunities arise Paratrici and Marotta will pounce on top quality youngsters. As they have for past years. They elevate their goals and ambitions for signings gradually ever since the quantity of mediocrity when starting out, we should defenitely be confident they will handle this well. Only thing we should question is their ability to sign quality AM
P.S I did not mention the only really old player we have Gigi's replacement, simply because its insane task for any sporting director to try address replacement for...and also because Gigi is a $#@!ing highlander. He can retire anytime he wants