It shouldn't be. The only reason it would be is incompetence.
The Everton hierarchy love an excuse. Let's not give it to them by giving them an out straight off.
New man should be in by the end of June. Brands should be transferring demonstrable failures out of the club at the same time. Big signings should be happening in July. New manager should be told that he gets us Europe or a Cup or his position will be reviewed at the end of the season. Mitigating factors would be derby wins, style of football, and a measurable sense of progression.
If Everton really want to bridge the gap to the top, they've got to stop being soft touches. We'll have a very good idea next May if the new man is any good. We could have predicted Koeman and Silva would be duds before they arrived. Some of us did. Carlo brought us wins at places we hadn't won at in years - as we felt he eventually would. Big Sam kept us up playing Big Sam football - as we knew he would. The only real surprise over the last decade was Roberto having such a stellar first season - but he was a busted flush by the time of a 3-0 defeat at Southampton before Christmas in the second season. And then we left it drag on for another 18 months...even though we knew he was spent.
The new guy needs to win us a cup or get us into Europe or both. Anything else is treading water. If he doesn't think he can do that, he should do an Antonio Conte and say "I am not convinced". We need fellas who are genuinely convinced they can do this. More to the point, we should be convinced they can too.