"Nuh Uh! Manabox Says It's A 3!"
So yeah, it happened to me. We have our pre-game conversation and settled on 3s. The guy on [Nissa, Resurgent Animist] admitted that his was "on the line between 3 and 4." I pulled out trusty old [Zedruu] for a nice, chill game.
The game ended on turn five with the [Emmara, Soul of the Accord] player tapping the [Halo Fountain] he'd cast that turn for the win, barely pulling it out from Nissa's 27 copies of [Scute Swarm] and assorted elementals. Meanwhile, the [Giada] player had nearly killed Nissa with commander damage and had close to 20 flying power on board.
After the game ended I said very matter of factly, "Y'all." (We're in Kentucky.) "None of those decks are 3s." Nissa and Emmara's players laughed sheepishly, but Giada's player said, "No!" and immediately started scrolling through her phone. I gently reminded her that apps can only detect decks that are higher than 3s if they have a certain number of game changers. She ignored me, then stuck her phone in my face and said, "See?!" On the screen was Manabox rating the deck a 3.
And I just. People. We HAVE to spread the word that the apps do not tell the entire story.
EDIT: I want to point out two things based on the responses.
First, the article specifically says 3s shouldn't be winning before turn 7.
Second, the part of the interaction that bothered me wasn't that I perceived the decks as being out of tier (whether they were or not). The part that bothered me was the immediate response of, "Nuh uh! The app says it's a 3 so it CAN'T be a 4!"
The reason I consider that problematic is because this person wasn't thinking about their deck and considering it in the way the article discussed. Instead, they took a number an (imperfect) app gave them and quite literally stuck it in my face. That's certainly not how the bracket system should be used, but it's how it's going to be used if people don't have conversations about it.