Isayama's manlet is great. Ever since I read Isayama's material I noticed they removed a lot of things. For example, the ACWNR manga removed some parts like with manlet, Isabel and Farlan winning against an old man just for tea, or how Hanje met the trio. But iirc they removed manlet's thoughts about him wanting to go to the outside based on Isayama's comments, got removed in the ova
You already know how much they removed in season 3, but they also removed manlet telling his motives and how he would become a monster just so the humans can have a chance to go outside. Looking at the WIT team they just tried to make manlet a Mikasa 2 but with Erwin, when according to Isayama manlet spends time with his subordinates, fooling Erwin to buy black tea for his people, cleaning but mostly training.
They also made Mikasa even better by screaming EREH when in that arc she was learning to be calm and trust in others a little more. Manlet and Mikasa fighting in serumbowl was also to compare how Mikasa in the end, even if she said to follow manlet, was too emotional for her friend