So the thread is talking about which champions are the hardest to master, as in which champions have steep learning curves. Singed may have a steep learning curve, but learning curve is not the same as high skill-floor, as he is easy to play difficult to master status.
Your original posts seem to imply that he is somehow difficult to play in general, which is simply not true. I still disagree with the characterization that Singed is a steep learning curve, his recent changes particularly as well as some of the past reworks have taken a lot out of that kit.
Furthermore the comments seem to indicate that what they are talking about is the difference between the base and ceiling of the champion, and that players who are good on a particular champion are much stronger than ones who are just average on that particular champion. The gap in skill between the floor and the ceiling, implying that he isn't a high skill floor but rather a high skill ceiling, which is something that I would agree with more than anything. Champions that have less going on tend to have a larger gap in higher skill tiers/between basic play and mastered play, because those players have to do more while working with less.
None of which you imply in your initial post either through miscommunication or such.
So if you are of the opinion that singed is generally very basic to get into, but has a steeper learning curve required to take your game to a higher level, then yes I agree. That's a philosophy I have had for many champions I play, champions with specific and limited types of kits tend to have these steep curves to higher levels of play. If you are trying to say that Singed is generally hard and that the skill-floor, or the base level of skill required to play said Champion is high, I disagree with entirely. he's easy to learn, difficult to master.
Furthermore what they are specifically talking about is this: http://champion.gg/champion/Singed/Top?league=platplus
There is a chart there called Win Rate % by Games Played, and they are referring to the difference in winrates as experience increases, certain champions spiked over time while others did not. The problem with that resource though is that it's taken from individual ranks, so you'd have to make decisions based on whether you accept all data from all ranks, specific ranks, combine that data, etc. This also only takes into account the current season. It's interesting though that some champions actually start doing worse with a lot of games played. So there is that as well.
I'd say it's a pretty big stretch these days to call singed high skill.