All users of the Rockwell CIP services for tag access will suffer if any element of a data type or AOI is set to "External Access: None".
Additionally, users of the Rockwell CIP services for tag access that strictly follow their published instructions (the linked data access manual) will be unable to optimize AOI data types and I/O module data types.
Rockwell uses undocumented services with its RSLinx drivers that I do not think any other company is using. But I haven't looked closely at what Kepware does. But even without those, there are opportunities for higher performance.
IA has a policy against using reverse engineering in drivers, where I do not. Ergo, my module's speed advantages due to looking under Rockwell's hood. So to speak.