Stonewall has a good intro video on why balance is hard for some champs.

https://www.youtube.com/watch?v=EhA7rxDV5XY

In case you are wondering why riot can't fix certain champs, this is a good 101 course on what's going on. Some champs are too simple. Some champs have too much going on. Some are too good to easily balance or too unique. However, none of this explains how cass's rework was messed up so badly.

One thing however is I'm shocked that Leona was meant to be a solo lane tank who can't jungle. I'm not as shocked riot let her be a popular support considering she was meant to go it alone because riot doesn't seem to care when non-supports go support but hate it when supports leave their lane. I'm also shocked she was meant to be solo lane with that passive. I think this is proof riot has no idea what they are doing at all and don't get the idea of cause and effect in design and balance their champs by RNG. No I'm not taking this back because they've turned a lane bully into the most passive champ in the game and assassins into tanks because reasons. What part of locking your damage into a passive that needs an ally to be present screams "I'M A SOLO LANER!"? No the bloody jungler isn't automatically going to gank for you and with the way she's balanced, she's a lose more solo laner.

See, this is also a good lesson on how most champs turn into supports when they aren't intended to be. Riot designs them completely wrong but so long as they don't need much gold and can do something useful bottom (usually just warding with a little CC), even the worst solo laner or jungler design is a viable support. _ I accidentally created a support_ aught to be a meme in riot HQ.