Right now if I have --use_global_long_query_time=1 I see:
| use_global_log_slow_control | none |
| use_global_long_query_time | ON
Whis is confusing in understanding how these variables work together and makes hard to check the status from scripts.
I would suggest enabling use_global_long_query_time would simply add the "time" to use_global_log_slow_control and setting it to 0 would remove that in this case we do not get into situation (and explainiung) what happens if you have global time check enabled in one of them but not other.