Master Yi is suppose to be based around speed but he only gains 25-45% bonus movement speed on Slowlander. That hardly matters cause other champions either have more movement speed than him or have some sort of mobility or crowd control so he many times he have hard time stick to them because of that. He got no utility that benefits the team and the only thing he brings is damage.
The kayle update grands her 15% movement speed when she moves toward enemies and up to 50% (+10% per 100 AP) on Celestial blessing. She can also heal and makes herself or ally immunte to damage for few seconds. She got slows, true damage lategame but also shreds armor and magic resistance and does damage based on target missing health.
Morgana on her ultimate gains up to 50% bonus movement. Ekko gains up to 80% movement while he got shield, massive healing, slows, mobility and so on. Jinx 175% movement speed on get excited. Kayn gets 40-80% movement speed that can move through walls and gains slow immunity for that duration. Lissandra root, slow, stun, and mobility based ability. Zed and Talon get massive mobility yet can slow enemies meanwhile Yi as a jungler does not have any crowd control to gank lanes or any form of escape during laning phase. The list goes on and on.
Ain't fair when champions have such overloaded kits to be faster than champion who the only thing brings is damage and speed and since he got no crowd control he cannot stop them from escaping so he got hard time sticking to his target. Yi's speed does not matter cause like I said either they got more movement speed than Yi or other type of mobility based ability or crowd control that they can escape from him or just play around that and kite him.
Yi was about speed and damage without any other utility that benefits the team and yet champions with shit tons of utility have more speed than him while he has no way to prevent them from escaping. Ain't fucking fair!