There isn't a "split control issue," the split control setup is fundamental to the way the Airbus control schema works. Changing it would be a non-starter.
For me at least, it seems like the condition where both pilots are inputting control on the stick or rudder is always an error condition. Even if they're both inputting the same inputs.
The scheme directly contributed to the crash for two reasons; obviously if the co-pilot wasn't pulling back on the stick, they would have been able to get out of the stall. But additionally, the two crew members were spending crew resources on redundant tasks: both of them thought that they were the ones aviating and the other was in charge of figuring out why the flight computer seemed to be behaving badly. Possibly if one of them did dedicate their attention to the flight computer, they'd have figured out what the actual flight parameters were.
That seems like a crucial functional omission.