How old are the thousands of fish you see on YouTube? Even on this site you don't see many fish dying of old age, in this hobby the % of fish that live out there full lives is sadly very low.
As I said I know nothing about clown loaches, so couldn't comment, my view point is coming from black water cichlids, some cope better then others but most do suffer over the long term to varying degrees
Your still looking at YouTube and thinking just because a fish has reached a good size it's thriving, alot of cichlids reach a good size after 2 years but can still live for well over 10 years, and as I said earlier most of those fish on YouTube will never make it past 5 years old,,, not long enough to show the effects. But I do agree some fish the pH or hardness will have little effect just not all fidh
The most commonly cited tell tail sign of "thriving" is when fish breed.
Tons? Really? I've only ever seen one central with hith. South Americans though... Hith city.Tons. Again this supposed "water Hardness dogma" seems to me to be really just speculation that is readily accepted as holy when it directly conflicts with the realities of our hobby that encompasses millions of aquarists with hard water tanks and giant soft water fish..
I mean I can agree with you if you want but honestly I'd just be agreeing...... I don't actually believe that's true. Based on youtube alone and the absolutely giant soft water fish in hard water tanks it's hard if not impossible for me to believe soft water fish can't do well in hard water.