Plot holes in Kung Fu Panda 2

Rating: 6/10 (11 November 2018)

1. It seems first Shen wanted to weaponized fireworks because he was power hungry to conquer China as he was a evil psychopath, his parents was worried about him because of his evil nature and tried to kill all pandas too make sure the prophecy about a warrior of black and white as pandas would stop him to conquer China wouldn't come true, but other source says Shen wanted weaponized fireworks to impress his parents and business of Gongmen City at first. How can Shen become power hungry to conquer China because he wanted to weaponized fireworks or his parents exiled him who had nothing to do with China, kill all pandas if Shen didn't want to conquer China at first and believe his parents would be proud of him for killing all pandas and conquer China when they weren't even evil too and even let his cannon crush him if he want to conquer China anyway? Shen would at least get his will to conquer over a kingdom since he was at least a prince who are the only heir after his parents to conquer over their own kingdom, usually royalties who have and are jealous of their older siblings who are the next to rule over their kingdoms and advisers who dislike their job or never get any praise and honor, become power hungry and will only conquer over their own kingdom instead of entire country or the world that have nothing to with them. How could Shen believe his parent would be proud of him to weaponized firework and conquer China if his parent weren't evil too? Would Shen want to take revenge on his parents? It were his parents who banished Shen because he want to conquer China and massacred pandas, but why did Shen still want to seek revenge when his parents was nevertheless died before his return?
2. Why did Shen want to make an end of kung fu? Shen even was a kung fu master too, kung fu had nothing to do with his backstory, his main goal was to conquer China and kung fu could be useful to conquer China. Shen created a cannon that would put an end of kung fu, but it's not only kung fu it should make an end of if there are anything else are as powerful or more powerful than kung fu, as chi.
3. The kung fu masters seems more weaker. How could the kung fu masters believe even only one cannon could put an end of kung fu and conquer China and didn't even knew first that Shen at least had more than one cannon and could create multiple cannons quickly that they should rather stop him from doing instead and how could even Po believe a cannon figurine was Shen's actual cannon when and didn't even laugh just because of it was too small too put an end of kung fu and conquer China? Aren't kung fu masters smarter, too quick and has high strength to hit the cannons and wasn't there other more kung fu masters than just Po, Furious Five, Shifu, Storming Ox and Croc who could also go to stop Shen if they needed more help? Cannon is too slow and heavy to swing fast enough and can only shoot on one place at once if there are more kung fu masters than cannons and are in different directions, even Tai Lung was shown to be cunning and swift enough to avoid firing weapons and was able to defeat the Anvil of Heaven, the Furious Five and Shifu on is own, Tigress hit the cannon down to the bottom floor of Tower of the Sacred Flame, Kai easily defeated many kung fu masters by taking their chi on his own and Thundering Rhino didn't even dodge the cannon's fire. Shen must at least have kung fu skills and learn his wolf and gorilla army kung fu to defeat kung fu masters, Kai and Taotie could make an end of kung fu, Kai easily defeat many kung fu masters by taking their chi on his own and once Taotie created a machine that easily defeat Po, Shifu and Furious Five (without Tigress). Why didn't Thundering Rhino try to dodge the cannon's fire and how could the other kung fu masters survive blow from the cannon when Thundering Rhino who easily dies of just a one blow by the cannon when he was bigger and stronger? Po survived probably because of his enormous body fat. Wasn't most important to stop Shen from conqured China than to stop him to put an end of kung fu?
4. Why is Thundering Rhino's physical appearance different than in Kung Fu Panda Holiday? Why is shown in the credits of Kung Fu Panda 2 Po made the the Furious Five action figures when he was a child if he was fan of kung fu since he was a teenager and the Furious Five were just formed then as revealed in Secrets of the Scroll?
5. Why is not even shown or mentioned that Shen began his plan years before or it was lesser than 30 years ago for the panda massacre and when he was exiled if it was 20 years ago as revealed in Kung Fu Panda 3?