I’m actually pretty comfortable with them as Elite, ie a similar training level etc to a Christian knight, starting in childhood as a Page, then progressing to a Squire and finally knighthood at around 20. That approximates the training level of the Janissaries. The JHI are the same training level as the archers etc. Exceptional is mostly reserved for units like Bodyguards, Templars and Merguen. Those and the Dmtd Bekh Druzhina are all low availability, whereas Janissaries are Late Pros and can be recruited in much larger numbers, plus in later years especially they formed a very substantial part of the Ottoman armies.
When the Normans conquered Sicily they never had more than about 500, and did some pretty amazing things with them eg at Cerami 350 of them attacked around 5000 Muslim troops (from memory) and destroyed them. This was repeated over and over in the Holy Land in battles such as First Ramla, Jaffa and Ascalon, where often tiny Crusader forces routed enemy armies many times their size. After most of the knights went home after the first crusade, having fulfilled their vows (so much for the Crusades being a war of conquest lol) only 350 remained.
Not sure on the lock_morale, there are quite a few instances of. The Janissaries routing or being driven back, such as the second battle of Vienna. What could be done is make them highly_trained and disciplined and also Fanatic (like the Templars), being +2 attack but -3 defense, which is a pretty lethal combination.
Giving them light_spear implies changing them to a phalanx halberd unit, which is reasonable. It would make them less effective vs infantry but better vs cavalry yes, and involves a bunch of stat and animation changes - will implement cheers
They need more anti-cav.
Which other channels have you been watching. Invicta, BazBattles, History Time and Real Crusades History are good too.