If I recall, the Bradley kill on the T-72 was a (few) hit(s) on the turret ring.
Every tank, no matter how well protected, has vulnerable parts, even in the frontal arc. For example, the T-72 had a weakness at the driver's vision block, the T-99 redisgned the front hull to reduce this somewhat. However, one weakness many tanks have is the area right around where the gun sticks out.
The biggest strength for the Type-99, imo, is its modularity, specifically in the armour package. The design principle recognized it will not start out perfect nor ever be, but rather evolve as technology becomes available. Making upgrading the armor package easy will let it catch up/keep up far easier. You can clearly see those big lifting attachments on the turret's frontal arc armor. I bet, like the engine, it can be replaced in under 30 minutes in field conditions. Imo, FCS and electronics should be relatively easy to upgrade, as long as there is a standardized interface, hardware is just plug and play, and software upgrades are trivial. Now if they over-designed the gun mount in expectation of future gun upgrades, I'll be really impressed.