What makes you believe that Eddie Howe is so safe? If he can't lead the club to success, everything will be against him. Newcastle has some investor backing them who have a lot of power, money and they want the best for the club because it is their money and the value of the club fluctuates with the performances of the team so to say. I doubt that the people behind Newcastle are ok with failing to qualify for the Champions League. At least I would not be shocked if Howe gets sacked at some point. I don't know if they give him one whole season, but for now it doesn't look good for them and the Champions League qualification is so far away that the chances are close to zero.
Newcastle have spent quite a lot to make their readiness in a good position and are considered one of the dangerous clubs in the last 2 seasons so it is certain that when the conditions are not in accordance with the desired expectations, the coach must be ready to bear all the decisions because it is certainly the coach who will be targeted because he is considered unable to advance the club.
Howe can get out of this trap if he is able to improve Newcstle's performance but if in the end he cannot do that then he must be prepared to leave.
You are right about almost everything but one thing is wrong. You said that Newcastle United spent a lot to get the team ready for the fierce competition in the Premier League, but that is not right and it is something I criticize. Newcastle would have had the money if they wanted to, but they spent only £130.8m and their net spending was £88.6m.
They are pretty much in the middle when it comes to their spending and I think when a club qualfies for the Champions League and has played such a great season, they should make sure that the squad is competitive the next season. That's where they saved too much money in my opinion.