I'd consider it a Linux bug if the kernel drivers don't transparently hide high color depths and refresh rates that aren't supported by the display/cable/GPU's maximum supported DP data rate.
DisplayPort cables don't have identification chips inside them. The only way for the machine to know if the cable is capable of running at DP1.4 speed is to try to bring up the link at that speed. The software does correctly hide modes that the endpoints say they cannot support, though that won't help when one endpoint lies.