You just keep ignoring power and depreciation like you have all thread.
And you use one guy as an anecdotal example and you wrote "user buys coins with euros, made a calculation error" which is HIS mistake. Whether it's the proverbial fat finger or a calculation error, it's HIS mistake and thsu HIS fault, not the system's fault. Furthermore, as I already argued, if he got lucky instead of unlucky and made a fortune, would we then conclude that buying is always better than mining? Of course not. It's just one (un)lucky guy. So we should not conclude that mining is always better than buying, or vice versa, based off one guy.
(I have never advocated for buying trashcoins btw, those are even riskier than bitcoin and litecoin. Only a completely reckless risk-lover would blow his whole wad on one risky bet on trashcoins. They are all correlated with bitcoin anyway so if you want to invest in cryptocurrency it's probably best to just stick with buying bitcoin and ignoring the rest.)
I crunched the numbers earlier and using YOUR numbers, assuming average USA power prices, you'd have to spend about $7.5k to get 50,000 litecoins if you had started mining on Jan. 1, 2013 through December 2013. (YOU estimated 50k coins, I was skeptical but we used your optimistic numbers.) If you had instead spent $7.5k on litecoins instead, you would have gotten over 714,000 litecoins. Which is more: 50,000 litecoins via mining, or 714,000 litecoins via direct purchase? You can do similar calculations for previous years as well like 2012. Miners made some money, but those who simply buy and hold made 10-20 times more money than miners. And they didn't even take on that much risk... in the example above, you could spend $700 on LTC and simply hold them, or you could spend $7.5k and painstakingly mine them as difficulty went up, and you'd wind up with the same result. Except the guy who bought them would not have to deal with mining headaches like heat, power bills, replacing broken parts, and assuming liability should anything go wrong.
The breakeven point for risk is about a month of mining, for a typical small-scale mining operation at average USA power prices. At that point you no longer have new GPUs to sell or return so you already have some depreciation, and you just ate a month's worth of power costs. After that point, if coins somehow go to zero, you are just as screwed as the guy who bought the coins directly, and possibly even more screwed depending on how much you pay for power. This is due to the high upfront costs of mining equipment, plus monthly unrecoverable power costs. It gets even worse if you have to pay rent or replace broken equipment. And obviously catastrophic mining failure can claim rigs, homes, or even lives, whereas there are no catastrophic buying failures. Even the wallet risk is the same either way--either you get hacked or you don't, regardless of whether you are a buyer or a miner.