Think about it.
Sonic Wave > Crescent Strike Resonating Strike = Lunar Rush Safeguard = Pale Cascade Cripple = Moonfall
On top of that, Lee Sin has superior mobility, isn't gated by mana, and can do the insec.
Conclusion: Diana can haz buffs plzkthx?
Diana was not chosen by Riot to be viable this season. Try again next season! #Riot"Balance"
Crescent Strike doesn't send her careening at the enemy with the same ability slot being pressed again. She has to burn more mana, and her ultimate, in order to do so.
I'd like to think that Pale Cascade is actually a superior form of Safeguard, given that Diana spends a bit longer in the middle of an enemy team at one time due to her lack of escapes. It also provides some healthy AoE damage that scales really well.
Not even a little. Cripple is a debuff that also deals mass AoE magic damage. Diana's moonfall stops her movement, knocks enemies up and slows them a bit, but adds nothing to her damage output.
Your comparisons are honestly just awful. Diana isn't a watered down version of Lee Sin, she's someone who's designed to be mobile enough to get in and go hard, not to get in, get a few hits, and then ward jump back to safety. You really don't seem to understand Diana's kit very well. I personally love her, she's quickly become one of my favorite junglers since two or three early points in her W lets her stay in the jungle for a LONG time, and I go incredibly ham with her through the mid and late games, as opposed to a Lee Sin who starts falling off in the mid and is reduced to a gap closing tank during the end game.
Diana's just fine where she is.
Except Lee's shield doesn't deal AoE damage, nor does he naturally build a stat that enlarges the shield the way Diana does. His q also doesn't do AoE damage, so it's pretty different in that sense. Lee is arguably a better duelist, but Diana is a better teamfighter overall. Yes Lee is more mobile, but Diana does more AoE damage and typically takes less while maintaining her high damage, where Lee has to sacrifice damage for tankiness.
Diana is about as far from Lee Sin as two champions can be. Having a gapcloser and a shield doesn't make 2 champions similar.
If anything talk about how Diana is a worse Akali.
In that they're gap closing bruisers, they are similar. However, Diana scales significantly better than Lee, even if she doesn't have quite the same monstrous early game skirmishing power he does.
I'd rather Diana not return to her old status of being the best initiator in the game.
In my opinion, with her current kit she can exist in 2 places. Either she is a worse version of Akali or a moronically monstrous assassin/bruiser hybrid that immediately kills anyone her Q touches and then packs a punch after that - while bringing some bulkiness and utility to her team.
Nope.
let me see.....
and have another lee sin? no thanx
lee sin has the effect that teemo has on the game, toxic Id rather not have another FOTM mini female lee sin she can stay trash tier hopefully sin will join her one day
Dont forget Diana's passive somewhat resembles a Lee Sin's passive, just in terms of the bonus attack speed :p
I have been playing against a few diana's recently and she is actually really strong.
Lee also has slower clears, weaker scaling, and (technically) weaker CC. Apples and Oranges.
Hamstrung, mana-gated 
even then, not really. Akali can't brawl, just assassinate multiple targets. Diana kinda can.
But lees sin take skills to play and have a lot of method to outplay enemys. Diana is a skill less champ and is boring.
