Short term impacts are easy to make, especially if the club has no midweek distractions. 2nd seasons are much harder, and it's much harder to manage when you are in Europe and have to deal with fixture congestion, normal injuries that occur due to fixture congestion, fatigue, loss of form, loss of time to train between games, etc. I'm always hesitant to praise a manager too much until they show they are able to perform well in successive seasons and while dealing with congestion and still putting out good performance levels. Results don't need to always be there, but keeping the same style of play and showing a high level of coaching is important.
Howe hasn't shown that, will take time for Ange to show that. De Zerbi has done pretty well imo, along with obviously Emery in the past obviously has done great with this.