Changes to stealth were a huge indirect buff to Lee
All the anti-fun element aside (R+flash to change directon is the ultimate "I'm loved by Riot and I'm making the plays here, not you" statement), there's a legit reason for Lee becoming obnoxious in the preseason. And that is his one unique trait in the game - no, I don't mean wardhoppping around like crazy - the AoE true sight.
Tempest is indeed one of the 15 abilities in the game with a true sight reveal. One of the other 14 is Sonic Wave, by the way. However, unlike every single other ability on that list but one, Tempest is not single-target. The only other ability, aside from traps, that could be described as AoE, is Twisted Fate's Destiny, which was once considered the hard counter to Evelynn's roaming with its global reveal.
Changes to stealth have removed all other counters season by season: first the red trinkets, and now even the pink wards. Vayne's supreme reign over solo queue is caused in half by her idiotic burst damage with two items, but in the other half by the fact that she can consistently get to that point by having free unobstructed stealth.
In a way, Lee's obnoxious pickrate and undeserved winrate is a direct consequence of stealth changes. Lee is right now the single best champion to counter Vayne, since she isn't losing lane all that hard anymore. And obviously the stealth reveal works quite well against the likes of Kha'zix and whoever else just got their stealth buffed to Invisibility.
Obviously there's also the factor of Red -> Krugs -> lvl 3 gank the lvl 1 botlane, and Lee Sin is one of the best champions to snowball an early lead. But the stealth problem is an important factor as well. Honestly Lee has always been bullshit, and the preseason only made that more annoying that usual.
There are two ways to fix this. One is to remove the AoE true sight from Tempest, which was already stated by Riot as one of the possible solutions. The other option is to simply finally nerf him in the other aspects - such as damage numbers or the cooldown of Dragon Rage - and leave the AoE true sight as his unique strength.
