The worse point is when this is pointed out to Riot (as has happened) their reply just makes you scratch your head. When talking about the nerf to Chilling Smite.
Riot Meddler said:
This might well end up increasing the difference between mobile and immobile junglers. If so that's all the more reason to look at whether certain junglers are too strong (not sure about the Balance team's current thoughts there).
And as we see from PBE changes (Veigar over all nerf, changes to Mord, Xerf nerf, Kass nerfs, making Nid a terror in the jungle) they don't mind changing things. Even if they are just tests. But we never see a Lee Sin test...
When talking about the gold increase on jungle items (to prevent snowballing on first blood before minion spawn) Riot Fearless said this about Lee Sin:
The actual reason why Lee tends to due really well through many rounds of changes is because he's incredibly flexible, very poorly stat bound (can do well with a huge range of builds), grants a lot of power that cannot be repressed through systematic changes. As stated above, he needs to be changed, and we know that many functions of the jungle changes won't be realized without those changes.
Just two small examples. As there are many more along the same lines. But it comes down to "we know Lee is bad for diversity but don't really care at the moment to look at him".
Really this pattern invalidates Riot's claim that they do not play favourites for champions.