Dear Riot, Nobody wants to lane against
or 
First, let's start with 
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Doesn't matter how badly you destroy him in lane and stop him from farming, he immediately changes the laning phase on you at level 6.
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Literally is triple damage on the next basic attack.
is double damage. Problem is, his basic attack is a Siphon strike. That's triple damage on a stacking ability. There isn't enough armor in the world to counter that. I've seen Rammus/Malphite be melted because they can't 1v1 him either, but that probably is contributed more to his ult than his Q.
The math
84.5 (base damage at level 6) + 70 (Siphon Strike level 3) + 75 (23 stacks over 7 waves including the 2 siege minions) = 229.5 damage +
(100% base bonus) = 314 damage per Q.
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The infamous level 6. There are a lot of ultimates in this game, almost every champ has one with the exception of about 5 (the exact number is irrelevant). Nasus is the only champion in this game that allows him to be 0/2 to his lane opponent with 30 less farm, activate his ult and kill you! You go from being the oppressor to the oppressed.
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The obnoxiously high passive life steal on a tank with consistent burst physical damage (Siphon Strike) gives him way more sustain than any champ should have. Even
can easily be dealt with utilizing

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Wither. MS slow and AS slow to an extreme.
Nasus specializes in dueling, Siphon Strike and Wither, but also specializes in AoE damage with Spirit Fire and Fury of the Sands. Though I hate Nasus, I admit he's manageable with many matchups against his favor, proof being in his low overall win rate. < 40% professional play (esports) 48% P+ Right at 50% for all other elos
On the contrary you have
66.7% pro
53% P+
> 52% all of other elos
Checked all the way back to S2 when I started the game. Singed has never fallen below 51% win rate! NOT ONCE! That's in every elo from Pro - Bronze. Being he's the only champion in all of League of Legends that statement applies to, that's a clear sign of being imbalanced!
http://champion.gg/champion/Singed/Top http://na.op.gg/champion/singed/statistics/top http://www.lolking.net/champions/singed https://lol.gamepedia.com/Singed/Statistics/2018
Singed is the only champion in League that always requires a team effort and strategy to deal with if your team wants to win unless he's hard countered by

Fortunately, there's an easy way to bring Singed in line. Move speed reduction while Q is being channeled. No reason he should running as fast as Sonic the Hedgehog while doing uninteractive damage.