wasn't the beaches defended by like 100 destroyers IIRC that would be more than enough to smash the southern force
Oldenrorf had 27 DD with him (including a couple RAN ships)
The "Taffy" groups had a total of 9 DD and 14 DDE
The "Northern" attack group has 24 DD
The "Southern" attack group had 28 DD assigned.
The "Close Cover group", flagged by USS Nashville added 7 DD (2 RAN).
It is, however, very important to note that the assigned number does not necessarily match the "present" figure at any specific point in time. A number of transports had already unloaded and cleared the anchorage as early as sunset on D-Day (Oct. 20, 1944), in some cases a destroyer or two was detached to escort them out of the area (as an example TG 78.3, consisting of 16 APA and 3 AP departed before sunset on the 20th with two DD as escort). Adding to the difficulty is that often one of the two escorting DD would be detached and ordered back to the anchorage once the area of highest threat was cleared.
There are two important issues that need to be remembered:
1) the DD force was extremely large, however the units assigned to the Surface Bombardment Group had expended most, if not all, of their torpedoes during the engagement in the Strait, so their combat power, especially against capital ships, was much decreased
2) By the time the IJN forces arrived more than half the transport/amphibious shipping had already cleared the area (TF 78 had entirely cleared the area save one cargo ship by sunset on the 20th) but follow-up "reinforcement" shipping was also arriving on a round the clock basis, but with the goal of clearing the anchorage by sunset each day. The potential "haul", even if the Yamato and her sisters had reached the anchorages would have been much smaller, and much less crippling, than is sometimes imagined.