@Egil
I don’t mind the boat mission, and honestly every Mario game has some unskippable butthard stages.
In fact, looking back, the original SMB was in some ways more unfair then “Lost Levels,” (despite being easier) because it didn’t have as many hidden 1up mushrooms, and sometimes the hidden 1up blocks would disapear if you missed a coin in the previous World: X-3 levels.
In fact, “Lost Levels” World 8-4 actually has hidden power-ups, allowing you to beat it as Fire Mario, unlike the original SMB. (Lose one life in World 8-4, and no more powers for you.)