1: It can make a huge difference, wukong wont be able to juke, you know which direction rengar is coming from and can easily exhaust him before he can burst, kha uses it as an escape so having sight on him makes his ult only good for refreshing passive. Invisibility is a big part of many champions' kits, having a trinket to render that useless is a needless nerf. Group up to not get assassinated, you don't need a hold my hand trinket.
2: You never needed it in the first place. You spend money holding pinks to use and negate part of an enemy's kit, it's a decent trade off. As the game progresses, no, you won't get to hold a pink. As pinks start dying and no one has room to replace them, vision starts disappearing off the map and it's easier for someone to get caught out and lose the game thus bringing a long game to an end. It's part of the game design.