So I can't really jive with the people saying "dial back your plays" to make the game more fun. I had a group I played with for several years and one player was CLEARLY better than 90% of the rest of us, myself included. Whether he was playing aggro decks or combo decks or brutal control/stax decks or one colorless deck (back when RoE first came out) that could slam it's general Kozilek, Butcher of Truth, with haste on turn 2-3 with some level of consistency. Rather than saying, "You need to dial your decks back," we started changing ours so that they were able to combat the pressure. He also offered really constructive criticism and card suggestions to make our decks more powerful. By the end of a few months, we stopped having games that were 15 minute blowouts where there was one obvious winner from the beginning and started having games that were going on for an hour or so. It made the entire group "more competitive," but it also created a more fun atmosphere where no one was pulling punches and everyone felt like they were giving their all but still remaining matched. It just feels weird to say, "Don't do this thing you designed your deck to do because everyone else might get upset."
As to the OP's question, no it's really not a faux pas, at least I don't feel it is. It either ends the game pretty solidly for everyone and we'll just shuffle up and play another one, or someone is able to come up with an answer (cheap removal, bounce spells, blockers, etc.) and the game continues from there with a very clear target. Now it sucks if someone gets knocked out from the get go, but in theory the offending party will also be knocked out pretty quickly, and then the two of them can play some quick games in the interim.
As to the OP's question, no it's really not a faux pas, at least I don't feel it is. It either ends the game pretty solidly for everyone and we'll just shuffle up and play another one, or someone is able to come up with an answer (cheap removal, bounce spells, blockers, etc.) and the game continues from there with a very clear target. Now it sucks if someone gets knocked out from the get go, but in theory the offending party will also be knocked out pretty quickly, and then the two of them can play some quick games in the interim.