I never got the appeal of achievements in the first place. I see them more as friendly reminders than something actually worthwhile pursuing. Chasing them is only making things stressful and tedious, oftentimes annoying and grindy. That’s kinda the exact opposite of any of the reasons I play video games for in the first place. If you want to use guides to get that 100% completion badge, do it. But if you ask me, your question means that you’re letting other people tell you how to play your games on 2 different levels: first by the devs in telling you what “completing the game” has to mean for you and now, secondly, by strangers on the internet in their opinion about which ways to get there are appropriate. Play it the way you want! If you want to hunt achievements because it’s fun to you, do it! And if you feel like referring to guides to get there, then do that, too!
You forgot about ties. They’re rare, but they happen, and in this scenario they work like the 0 in Roulette - they fuck over your nice and comfy 50/50 chance.
And as others already mentioned: I’m pretty sure that whole scheme wohl just be plain fraud.