Well, from a moral/ethical perspective I completely agree. Cheating at or exploiting bugs/design issues in an SP game is no sin, and is entirely up to the owner of the game. If that person then goes around making claims about the game, having done that, but without disclosing it, well, that’s mildly unethical/dishonest, but I wouldn’t say you’re doing that.
However, on a literal level, obviously you CAN exploit and cheat at single-player games. Whether this is an exploit, YMMV. It’s not a bug or error per se, just bad design - and it’s not even terrible design, because the chance to be hit tapers off to very low numbers before disappearing entirely, as I understand it. What they should have done is simply capped Dex-based avoidance of attacks/effects at 90 or 95%, imho. But they didn’t!
So long as you’re not going around making claims about the game, or other players, or whatever, it is indeed so.
Talking of making claims about games, I am back on TW3, and it’s a frustrating game, simultaneously brilliant and boring, overstuffed and understuffed, and actually more similar to Skyrim than I thought it would be, based on the hype before I played it. Still, even it’s dodgy quests are better than a lot of Skyrim radiant quests, so there is that. I just wish there weren’t so many of them so haphazardly scattered around. I know I don’t have to do them, and I’m sure I’ll skip some, but the fact that some are really good is kind of a problem, because I continually worry that if I skip some rando-sounding quest, it’ll turn out to actually be something awesome!