If you can't watch the program due to language barriers I cannot provide the most accurate explanation because it involves the entire history of tank development in China.
Summary of memorable points from the three parter - Type 59 had a lot of Soviet lineage duh. English gun L7. Excellent gun and manufacturing technique for the steel and barrel making from the English. French gun less capable (AMX 30's). Pursued a more western philosophy except China didn't have the industrial capabilities back in that era to match western metallurgy and new advancements of welded turret. Every new development was done but diverged a lot. Every time they got a chance to see results of philosophies like Gulf wars, they realised their development is no longer good enough. Russian Soviet ammunition is poor and so if Chinese. Russians first used 125mm to compensate somewhat using brute force. Chinese experts knew the 105mm is actually really pretty up there and just as good. Chinese ammunition of those years were also too poor. Ended up pursuing similar method... both also used tank launched missiles after all to also compensate. Interesting point lol - says Chinese loaders were not as strong as westerners not built as well (back in those days of famine) and 125mm is much heavier piece of ammo than 105mm as well so more reason to go with autoloader. 105mm still top shelf stuff and with the right gun mods and barrel performance, can deliver satisfactory energy behind an armour piercer. Of course 125mm will have high pressures and power still but 105mm isn't really that far behind. Also talks about lighter and smaller caliber guns being easier on fire control and accuracy obviously which means heavier needs higher power mechanical equipment to stabilise aim (my interpolations).
T-80 when they got from breakaway soviet independent states surprised them. Realised the Type whatevers back in the 1980s/90s wasn't good enough. That was a period of lots of prototypes and trial platforms. Eventually Type 98 and then talks about the history of that lineage developing from 98 to 99 (early type) and then 99 (second type) and then 99A. Also mentioned in the first part that T-72 they were surprised at how unthreatening it is (not sure how they determined or forgot what he said) basically at some point presumably in the 1980s they discovered T-72 was weaker than they thought. T-80 however showed them Chinese tanks of that era were behind the curve which resulted in further developments. I'm sure Gulf wars also motivated new tanks like Type 98 and onwards.