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Principle is right. Charger will only see pack voltage (in most cases) and switches between full current/reduced current based on voltage information. It doesn't know if some individual cells have different voltage than others. When pack voltage reaches certain level charger will start to reduce current on its own. BMS might tell charger to ease a bit if certain cell voltage is reached or even tell charger to cut off completely.
If main goal is to have all the cells at same voltage in the end of the charge one should perform top balance separately for each cell. Ideally none of the shunts (load across the cell) shouldn't get activated during charge process and charger should finish the complete charge on its own. Only if some cells go out of balance and try to reach unwanted voltage levels should shunt resistors activate. And this should happen during recuded current charge. Pack requires manual balancing if BMS trips charger before it starts reducing current.
Shunt resistors will get hot when they are in use. If you want to remove more charge from a cell you need more powerful resistor. Then it gets even more hot and requires a big heatsink. It is not desirable to keep them on for a whole charge. It is all wasted energy there. The less you need to use them the better.
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