No, on all of timelines, finality, and who makes the final call. You're making very confident statements about a complicated process you don't seem to know all that much of.
> After a week, if the merchant doesn't object, the funds are released to the issuing bank. [...] it's ultimately the issuing bank (i.e. the customer's) that makes the final call
The funds are moved immediately, but within a given timeframe (depending on the network, but usually much more than a single week), the merchant has the option of clawing them back once again. That's called a "second presentment" (see for example [1] or [2]).
The issuer then has the option to submit a second chargeback if they still believe they are in the right, and depending on the type of chargeback, the acquirer (and by extension merchant) might get one more chance to send yet another response. If they are still disagreeing at the end of these steps, the case can be brought to the network, which then makes a final ruling, but that's very expensive (and the losing party pays), so it's usually avoided.
The money moves from issuer to acquirer and back for all of these steps. Only if the issuer makes the last move, and the acquirer does not challenge it, is the chargeback considered "won". All of that is usually hidden from at least cardholders via the provisional credit mechanism mentioned above.
In any case, your assertion that the issuing bank has the last word is simply not true.
[1] https://developer.mastercard.com/mastercom/documentation/get...
[2] https://chargebacks911.com/second-presentment/