Squad familiarisation and integration is so vitally important, especially so for a new manager working with wholly different setup and personnel. Even his own players will have to get used to working with a bunch of unfamiliars who are some way below the standards and needs of what the manager wants, and probably will still be getting to grips with it by the end of preseason so every day without them, is a far bigger concern than what's going on at our rivals for 4th place. It was far more imperative for us to get our house in order than literally anybody else, and yet here we are.
Chelsea's tribulations are not the same nor will new signings have as many teething problems because they have a manager in place who knows his squad and has an established system in place, plus a core group who know exactly what is expected of them. New players simply get with an established program, so it is nothing whatsoever like what we face and gives them more leeway - with less disruption - to sign players late and not have it mess with the natural order there.
There's a time and a place for patience, and in terms of this window for us, it never was there as we had the biggest bridge to close off the back of the worst season in the entire league (relative to both expectation and standing) with the newest manager and the most work to do to get a wholly new way of playing assimilated. This was never the window to espouse patience with transfers as it is tantamount to neglect; we needed the most time with new everything and this was known before the season itself had even ended let alone before the window had opened in any capacity. Patience for the manager trying to implement a new system with woefully undercoached players is the only acceptable one because it's common sense that that may well take longer than a couple of months.
What annoys me is the manager is being set up to fail by us not utilising the window effectively. The later players come in, the more overspill into the season proper; the more overspill into the season proper, the more potential for needlessly dropped points - points that mightn't have been dropped had all our pieces the time to familiarise. It then goes without saying that the consequence for a muddled start is crying at the back end of the season about 'if things were different', which by then is moot and a redundancy as the consequence is hard loss of cash and the opportunity to sign CL-level players without any impedance the following summer window. Everything is connected and it is short-sighted to think we can get away with it if not adequately prepared. Even our greatest manager knew he could no longer have any dalliance at the start of a season once the points bar had been raised, so it is bizarre to me how some don't want to acknowledge how vital preparation, in all aspects, is to the season itself.
Finally, ten Hag's players are supposed to be his failsafes - a comfort blanket of sorts. Players he can trust and depend upon to lead and guide others and have the confidence and competence to execute what he wants and remain steadfast and resolute within his system no matter what. By not having these players integrated, we run the risk of the players already here buckling or possibly reverting to type if initial results are not as hoped for - this is human nature and not something to blame them for, but it's also an obvious need to be contingent about; if player X or Y is really struggling and we can't take him out of the spotlight because we don't have the flexibility due to lack of personnel, it is entirely our own fault - you do not plan without contingency and failsafes and it's tremendously frustrating to have the manager placed behind the starting grid in this sense, particularly so when everyone around him is bringing a prepped and stacked arsenal/battalion to the same proving ground.
All is not lost, but our time to actually be locked and loaded for the start of the season is dwindling rapidly.
The tl;dr is as simple as: sort your shit out or suffer the consequences and don't dare complain after the fact (which will be whatever time in the season said lack of preparedness is irredeemable).