"stupidly difficult" to me means Nethack. You should try it if you're into rpgs :)
I like Nethack :) Btw, that reminds me of Dwarf Fortress and the whole "losing is fun" idea, of which I am a great fan as well, and do not find anything stupid about it ;)
I'm quoting from the linked Gamasutra post, which shows the attrition rate per level.
Sorry, my bad, I did not read this article. Zach himself is calling the game "stupidly difficult". I still strongly disagree with the term though :) Plus seeing the graph, I find that it does not seem to be the case - I mean most levels in the main campaign seem to be over 80% success rate (hypothesis: "defense" levels are not available in the Android version, which could be a reason why they seem to have a lower success rate)
80% completion rate with 20 levels works out as a ~1% chance of ever finishing the game (which i'd say counts as fairly hard). Looking at the graph, the pass rate seems to be higher, but there are also a lot more than 20 (non-optional) levels, so I would guesstimate the finish rate to be less than 1% (90% per level for 40 levels is also around 1% to finish the game, for example).
https://steamcommunity.com/stats/SpaceChem/achievements according to steam achievement "beat the game", it's actually 4%. I do agree that it makes it a difficult game to finish. Then again, my point is that I think it's fine not to be able to finish a game, especially a puzzle game which have no story. You just have to spend more time on the puzzle you are stuck on, so in a sense, you get more game time for your money :)
Honestly, I find that Spacechem is one of the very best game ever. I am really happy that Zachtrorics continues trying making better similar games, as it generally does make great games (I immediately purchase all their games - I only missed Opus Magnum as I was busy becoming a father when it launched), but so far, I was not able to feel the joy I felt when my Spacechem reactor finally worked, watching all the chucks fitting together (I know, I really need to try Opus Magnum which is more similar to Spacechem than other games in the serie - but my impression is that the UI looks much more busy, and simplicity is one of Spacechem strong point, which makes it enjoyable on a tablet for example). I'll admit that Spacechem had the advantage to be the first of this kind I tried, so it could be one of the reasons I loved it so much.
Also I am a bit sad that making games easier to beat is even a goal at all - it's great to try to make them easier to play / to start for non-programmers and beginners. But I find that having a few levels that are really challenging makes a game strictly better. I know that many people think "I paid for the whole game, I need to be able to finish it all reasonably quickly", but personally, I think it could just mean that the game was simply not challenging enough.
For what it is worth, I did beat Spacechem (whatever it means, I have the "beat the game" achievement on Steam), but I am stuck on TIS-100 and Shenzhen I/O (I spent much less time on this one though). Exapunks does feel easier than both for now (the programming language is slightly "higher level", so maybe it feels more familiar).