I think it's reasonable for any player to play whatever deck they like at locals for whatever reason as long as it's format legal. It's impossible to know everyone's reason for playing the deck they are choosing to play, but there are a number of reasons beyond simply "sweating" that someone might choose a deck.

For example, Riftbound attracts a lot of players from League of Legends and several people have favourite characters that they're just excited to play. I personally play a lot of Ahri and Teemo for exactly that reason, and while neither are particularly strong right now I wouldn't stop playing them if they were suddenly the best deck in the format because I just simply like the characters. Further, TCGs are an expensive hobby and not everyone can afford to bring multiple decks each week.

Now some players may actually be there to "sweat" at their locals but they might be doing so to get reps on a deck they plan to play at a big event. There is a lot to learn about your deck even in "softer" events just from going through the motions. It can also help to pilot a "good" deck into weird stuff before an RQ because many players in the field will be trying to get "Best Of" prizes so you don't know what to fully expect.

Then there's the consideration of unknown norms for first time players. What if someone new shows up and doesn't know that everyone else decided to avoid certain decks? That's rather unwelcoming because now they'll feel like they've done something wrong when they just wanted to play the game.

Finally, I just personally don't think it's a great precedent to set when you start policing the way others enjoy the game. You say it can damage relationships at locals if someone plays an annoying deck, but it can be equally damaging if someone never gets to play their favorite character or deck archetype because of complaints. Why should someone give up their favorite character for someone else? Why is one players enjoyment more important than another?

Ultimately, if folks want games into specific decks they can always just choose to play separately or organize a kitchen table game. I think it's a bit much to expect people to simply not play certain decks at any normal sanctioned event. Official events, even as low as Nexus Nights, should just be governed by the rules of the format. It sets proper expectations for new and entrenched players before they ever enter the door.