BMS or no BMS for LiFePO4?

Take a 12V LFP battery. Voltage Range is 10.0V (2.50 per cell) to 14.6V (3.65V per cell MAX)
You are charging the assembled battery pack at 14.0V (*theoretically 3.5V per cell).
Internal Resistance & Impedance will cause each cell to take as much voltage as they can BUT they will vary a bit.
As the cells reach normal settled "full state" around 3.425V per cell, innevitably one will "RUN" ahead of the others and reach the BMS Safety Overvolt cutoff (ususally 3.65V) unless programmed otherwise. THIS IS AT CELL LEVEL !
This will protect the entire pack based on any single cell deviating from normal.

IF there was no BMS, the Runner would continue to increase its voltage while the others are left behind.
You are still pushing 14.0V BUT now you have one cell @ 4.0V while one cell may be at 3.2, another at 3.3 and the third at 3.4.
That cell at 4.0 is BEING DAMAGED NOW... The whole "battery pack" does not know anything and will not stop till it is at 14.0V (if the Charger / SCC is programmed to stop there.
END-AMP readings would be of NO HELP because the IR/Impedance is skewed thanks to the runner and which ever cell is the weakling "Lazy".


Where the confusion comes from:
It all goes back to Lead Acid. A standard Lead Battery such as a Rolls S-550 which is a 6V Deep Cycle monster, has 3, 2V cells in one unit which is internally connected. If properly watered & maintained each cell within the battery will self-balance and stay level. That one battery will behave properly and the Amps taken is consistent and will decrease as it is supposed to as the battery reaches 0%. DOD (Full). With Multiple Batteries in in series / parallel the lead batteries will self-balance (more or less) IF they are properly watered & maintained. Over time the End Batteries (where the POS & NEG are connected) for output, will "tire" and start to lower the overall bank capacity. These should be manually rotated through the bank every 3 months but few do it. The lowest capacity cell will bring the entire bank down to its level, regardless, the weakling rules the roost. With Lead the End Amps value is taken from the entire battery bank as a collective measure. This cannot & does not apply to Lithium in the same way.

Far too many people do NOT understand that many of the "Lead-isms" do not apply to Lithium. These are NOT grocery store AA batteries !

Maybe this clears things up, maybe not.
Hope it helps in any case.
BTW: I run 956AH of Heavy Rolls Lead and within two weeks my final 280AH goes into the LFP bank for a total of 1,190AH.
Been at this for a few days, so just a wee bit of experience. /s