I'm not sure Erik ten Hag will quickly bring success to Manchester United, but if Erik ten Hag can really make good and fast changes then surely Erik ten Hag cannot be underestimated.
Well it depends on the kind of "success" we are talking about here, i am pretty sure the United board are pretty aware that no matter how much they invest this summer, Erik winning the EPL for them next season is almost impossible, United is more or less like a disjointed group that will take some time to fix, and it will take Erik quite some time to get the boys going again, they need confidence and hopefully he would be able to build it back again in the players.
Having said that, what would be expected of Erik is to make Manchester United competitors again, they have to compete like a big team, they were more or less whipping boys last season, and that really cannot continue in the new season, they have to start playing like a big team, with desire and will to win, that is the only way they can get back to winning ways and in a couple of seasons win the EPL again.