Klee's Burst stops as soon as you switch off of her, as far as I've seen in videos, though her little bombs do hang around. Regardless, they're both strong characters, probably #1 and #2 damage, regardless of order. I'm just saying if you're trying to get the most out of, let's say Diluc, Xiangling with her Fire damage buff, deployable elemental skill (that also drops an attack buff), and wide AoE persistent burst are probably bigger damage maximizers than swapping back and forth between Diluc and Klee. My Diluc gets his Burst charged so quickly I'm constantly having to wait for cooldown to use it again, I can't imagine having to switch to Klee would be a net damage gain.
Again, doesn't really matter though because they're both powerhouses and either of them can trivialize boss content.
So the Reddit hivemind have further discovered a way that JohnLee was nerfed. Apparently his normal attack string was supposed to be hybrid physical and geo damage, indicated by the animations and elemental sight on his attacks. If this was true, he would have been a monster at generating shields even more than he is now, and his Geo damage passives would make a hell of a lot more sense.