A monopoly on the North American high school market perhaps, but over here in Europe the NumWorks, Casio Graph 35+E II and to a lesser extent Casio Graph 90+E are wrecking TI's market share so badly that they had to release the TI-82 Advanced Edition Python (no rechargeable batteries nor USB-OTG capabilities in an old shell) with a significant price drop just to stay competitive. So they really had to do better, just not in the USA so far.
The modern replacement for a TI89 would be a TI-Nspire CX II CAS because both were/are high-end CAS calculators. But the TI-84 Plus CE Python in its american middle market segment is an embarrassment and an aberration only sustained by their monopolistic practices. The fact that they can get away with this for new graphical calculators at full price in America is just sad.
The modern replacement for a TI89 would be a TI-Nspire CX II CAS because both were/are high-end CAS calculators. But the TI-84 Plus CE Python in its american middle market segment is an embarrassment and an aberration only sustained by their monopolistic practices. The fact that they can get away with this for new graphical calculators at full price in America is just sad.