It's good to aim high, but it's also kind of pointless if there is no plan to get there. That's not a dig at United, but rather acknowledging the reality Arteta came into. He's made constant incremental progress, and he's done so in a holistic fashion. They decided the profile of player they would target, developing their playstyle as the quality improved, and overhauling the squad.The point is more Arsenal are not what United should be copying, if we want to return to our past status. We had some of the best players in the world in every position, the same way City and Liverpool do now. If we started signing Ramsdale, White, Tomiyasu, etc and finished 5th, that absolutely isn't classed as success. Even finishing 4th would have been a shocking season back then. Like Keane said after his rant when we played Spurs a few years ago, we're just talking about getting into the top 4 never mind winning trophies. 4th shouldn't be good enough. And yes I'm aware that in United's current state, 4th is the best we can manage. But that isn't good enough.
This isn't me being reactionary, I've gotten plenty of shit in this thread over the last few years for saying Arteta was heading in the right direction. You say that 4th isn't good enough for United atm, but it absolutely is. Names are meaningless (and clouded a lot of people's assessment of Arteta's early work), ETH will need a lot of time. It might take him a few years to get into that position. It's all good pointing out Arsenal went unbeaten a couple of decades and United won trophies every season under Fergie, but that has no bearing on the current situation and the current quality.
I'm not saying United should copy Arsenal, United are a bigger club with more options and they're starting from a different scenario. They should take note that things can take time though, and progress won't always be reflected instantly on the league table. There are a bunch of strong sides in the league, and the top two are almost unfathomably consistent and have the two best managers in the world with years at their respective clubs.