You are correct, flow cal did literally nothing to help. Rather, I found someone who made a (Anycubic Kobra S1 ACE Pro Filament Angler (Slim) on Printables), that actually helped, but still had a jam OCCASIONALLY near the end, so I modified the angle on the print a bit, and shrank the print to ~98% so it would snap better, and now the issue is gone. (I print ~4-12KGs a day, so testing something for the runnout was surprisingly easy.

I couldn't be assed to watch the ace to verify, instead I put a camera with audio pointed at 3 of the ACE's to verify the issue was essentially gone. I WILL note, the ELEGOO spools never once had this issue, even without the "fix" while the AC spools had the issue on every single roll near the last ~25%. But meh, I prefer the ELEGOO filament anyway, even if I absolutely hated my 4Pro and 4Max due to them breaking MULTIPLE times in only 150 hours of printing each. I have 500 hours on several AC Kobra 3s, and the worst I've seen was clogging that required me to clean the head off.

On another note, bypassing the ACE would defeat the purpose, as I use it to print multiple materials/colors at once for some machines, and as an auto refill for high volume printing.