Generally, for this purpose you need to use the UDL concept (user defined link), which defines a location with its link speed, through a config file. Then use "network link data" DMI data view. There you will find utilization column, expressed in percentage of the declared UDL speed. Use this one on charts and define high watermark as 100%. Actual bandwidth usage can be added as the secondary metric (or vice versa).
Surprisingly, I can't find the actual defined UDL speed as a metric in any DMI data view:-)
I see your point - but no, we don't plan any advancements in this direction. At heart, NAM is not a network monitoring tool, it is application monitoring tool with network awareness to the level required for fault domain isolation network vs server. But network links, topology and flows analysis is beyond our domain.