Open circuit voltage testing does not test the "health" of the battery only the state of charge. It is not the best way to test the SOC, a hydrometer is the best way, however with a sealed AGM battery that is not possible, so open circuit voltage is the only way to test the SOC.
The Battery Beak will give insight as to the health of the battery by measuring its internal resistance in addition to giving the SOC.
Yes battery mfgs base the AH rating on discharging to a loaded voltage of 9.6~10.5v but they do not recommend discharging the battery that low on a regular basis IF you want to maximize battery life. Here is the
spec sheet for the Enersys FRC legal battery, from team #955. Note on the first page the expected battery life based on cycles and on the second page the percent remaining capacity vs open circuit voltage graph. 1200 cycles for a Depth of discharge of 30%, open circuit voltage 12.2~12.5v vs 250 cycles with a depth of discharge of 100%, open circuit voltage 11.2~11.8v.