Who said that? That hasnt been the argument at all.
"42% of marketshare lost"
"86 million in isolation sounds great, but when you consider PS3 lost nearly half of PS2's marketshare"
"[PS3] gutted Sony's console marketshare."
"But, this completely ignores everything I pointed out about lost marketshare, massive financial losses which completely erased their own profits from their unbelievably successful previous gen, and substantial amount of lost customers. "
"PS3 still gutted Sony's console marketshare."
Yeah, no one has made an argument that the PS3 is considered "unsuccessful" because it never sold as well as the PS2. Nope. Never happened.
That's completely different than your previous comment though.
Mandalore & Curl (the people you are quoting) have said the combination of huge financial losses, huge marketshare loss and huge customer loss is why PS3 is seen as a failure.
Neither of them said PS3 was unsuccessful just because it did less than PS1/PS2. It's the combination of a few factors.