Demon's souls was never a presumed failure.
When people talk about DeS being a failure they mean the development. Apparently game was in a dev hell until Miyazaki took over and completely rehauled it.
And it was also a commercial and critical flop after the initial release in Japan. I sold p. badly and got 7/10 from Famitsu. Only with time it started to grow into a cult, first in Japan, then the US.
it has some dumb flaws, which I think we all agree on. From didn't improve what needed to be
DS2 improved MASSIVELY over DS1 systems-wise - armor, poise, split damage, weapon enhancements, PvP, best hub in the series, covenants, NG+, bonfire ascetics, respec (even gender change lel), humanity/invasion mechanics, grid-based UI, multiple item use, covenants, hard mode (champions stone), build variety, powerstancing.... and even that list isn't complete. Just tons and tons of improvements.
But yeah, there were problems with it:
- the world design - by far the most serious problem, linear instead of interconnected; people loved the latter, From gave them the former for some reason... and then again in DS3
- there was no Izalith or Demon Ruins but individual levels didn't have the DS1 heights
- soul memory - an attempt to improve matchmaking which made it worse
- ADP - another well-intentioned experiment that mutated horribly
- teleporting from the get go - the first step on From's long road from hardcore beginnings to appeasing crying and bubbling normies; people often say the best thing about DS1 was the level design but that's wrong; the best thing was the fact that you couldn't teleport around like a retard for the first 2/3s of the game