Lol that's super faulty logic there China hasn't managed to get a total buffer agreement out of India (only a partial one) means that India secured large parts of the disputed... lul mate. China securing a total buffer would mean India has been totally defeated on this dispute because then India wins 0%, China wins 80%, 20% buffer. More or less the same deal for demarcation China has offered India throughout the later half of the 20th century.
As things stand, India controls 0%-5% of total legacy dispute. China controls 80% to 85% of legacy dispute, 10% to 20% of it is in buffer (partial buffer zones achieved by China in exchange for China disengaging PLA from forward positions that India failed to thwart and failed to counter) and in nominal state - not buffer, no troop presence, but potentially patrolling from either side.
Aksai Chin not touched by India. 20% not controlled by India either. When you say no total buffer agreement managed means India secured large parts of the disputed. 1. This is faulty logic and simply erroneous. 2. Where's any evidence to support this? If India controls large parts of the 20%, India would be talking about to Pluto and back. Patting itself on the back every second. Shouting it from the rooftops of the English speaking internet. In truth, China and India hold similar levels of control over the 20%, remaining are either buffer or barren - no troops, not buffer, but also troop presence and patrol is allowed albeit with distance between troops... so both sides say.