Well, that's sorta good news. Back in the day, that issue was rooted in mechanical hard drive read speed, and I can't recall if AFS was a journaling file system like NTFS, like the one I still have in my 10 year old windows machine <left eye twitches>.
Speaking of which, sorry if I missed it, but what did disk utilities have to say about the version and health of the file system? Have you tried pumping the payload to a new drive, just to see if there's some sort of fragmentation or catalog corruption? I'm sure it's not a "FAT" formatted disk, but by any name, there is still a file allocation table in there somewhere.
I am not the original poster, but I have observed the exact same problem as she or he did. Here is my history and set-up.
Up until early July of this year, I was using a 2015 27" iMac with an i7 processor, a 1Tb internal SSD, and lots of memory. This was attached to two external storage peripherals via Thunderbolt. One was a 4 bay RAID drive using spinning hard drives. The system was formatted as HFS+ in three volumes. The other was a dock that allowed me to plug in nude SAT drives, either 2.5" or 3.5" size formats. I used the latter for a pair of SSDs used for Time Machine backups (they get swapped every week or when macOS gives me the 10 day reminder) and to back up not only the iMac internal SSD with Carbon Copy Cloner onto an SSD but also the RAID system onto separate drives for each RAID volume.
With that system, when I looked at one of the larger folders on the RAID drive through a Finder window, the content population was almost instantaneous. Same for when I wanted to Save As or Export as PDF from Safari. No complaints at all from me. Large meaning perhaps 1500 folder items.
Then, I replaced the iMac with an M2 Mac Studio. Lots of memory, and the same 1 Tb size internal SSD. This came with Ventura.
Using the same RAID system connected the same way it can now take up to 20 seconds to show large Finder window contents. Same effect when using Save As and Export to PDF from Safari.
At first, I thought it was because the new system was taking time to index everything. Nope. Same after a week.
Next, I suspected the RAID system. So, I tried plugging one of back-up stand alone volumes into the dock and opening a large folder in a Finder window. Same exact problem.
I even tried wiping the RAID system and starting from scratch using the back-up volumes. No change.
Since external applications like Carbon Copy Cloner can copy files at really high speed, I don't think it's a hardware problem.
The experiment of adding the large folder to the Dock and opening it from there gave me an almost instant content listing. That just further shows that it's not the hardware.
I think this shows that there was a significant change made in how external drives are handled by macOS through the Finder. Not a bug - a design change. I thought it might be for security reasons, but the folder in the Dock experiment kinda invalidates that thought. Then I considered that maybe it's an HFS+ versus APFS issue. Again, the folder in the Dock experiment nullifies that.
I don't think that Apple is much interested in revisiting decisions they made in their process based on customer wishes. Their history of late is that they only respond to problems that might trigger warranty repairs (iPhone 15 overheating) or give really bad press and maybe lawsuits. They only move forward in the directions they chose internally. Yeah, maybe I'm being cynical or negative, but I know that these are smart people. They HAD to have known what effects their change would cause. This isn't a subtle effect caused by some weird combination of hardware and apps not of their making. This is an operating system methodology.
. The one thing that stands out is that you said the issue was not limited to intel and that it existed on silicon. That I did not find in my tests. I have a very new MacBook pro with the latest chip and it 'seemed' fast. Notably the load of the large folder test it passed immediately. I did not throw a lot of video at it or run a blackmagic speed test on it but I will get to that and try. My whole concept in my head was upgrade to silicon and just move on since Apple seems to ignore the problem. That would throw that crazy 'work-around' concept out the window. Good cause it will save me thousands. But what I dont get is why apple ignores this. Users with large raids and doing lots of video work are the back-bone of their power users and I thought the reason their mac pros existed. Raids just dont like being formatted in APFS and apple even suggests against it with spinning drives...odd. Sad too. I will update you on the stores powers...Lets see. I will show them this thread for sure!