Charging the cells individually will take longer because of the human interaction delay in the loop.
The benefit is, your cells can settle individually which is another indicator of general quality and of how well the cells are matched.
Another benefit is each cell will stay in the high knee for a shorter amount of time as charge current is higher.
Finally individually charging the cells avoids the scenario where one or more cells spend a long time exposed to high knee voltage stress because the started out at a higher state of charge than their peers.
IMHO, the time variable renders cell settling variation meaningless unless you're willing to kill additional time.
8 280Ah cells, 14 hours average each to charge @ 10A. Assuming 1 charged every day. Cell 1 has 8 days of settling. Cell 2 has 7 days, etc. What does that tell you? I guess if you're willing to let all the cells sit for another 8 days. Now all cells need to be hit again individually to ensure they're at peak SoC because 8 days between charging could matter in terms of balance.
In parallel, could shave off a day or two and then let them sit un-paralleled for 7 days and have all of them settling over the same period. A little simpler.
As alluded to in the guide, the time spent in the leg is a small portion of the total charge time. The C rate of parallel charging is so low, there's almost no leg when viewed on the total time scale... just a little tick up at the end. Additionally, these big 280Ah+ cells have a very high settling voltage - essentially in the leg.
My experience with 20A charging of 280Ah Eve cells had the leg occurring during the last 20 minutes out of a 14 hour charge (2.4% of total charge time):
At 10A, that would be even smaller.
Assuming worst case that the ultra-low C rate takes the same % of the total time, 8P charging at 10A for 112 hours might spend a couple of hours in the upper leg. I can't imagine this can cause any meaningful issue with top balance or cell longevity.
At some point, precautions have diminishing returns. IMHO, this is one of those situations.