Personally, I don't really fault people too much for their durability when judging their strength. I look mainly at their arsenal, and Momoshiki's arsenal isn't so fodder. As for the whole losing a clash to a kid thing, that was due to Naruto's amping of the rasengan and possibly partially because of the properties of Boruto's vanishing rasengan (Naruto's amping and the properties of Boruto's rasengan are likely what enabled Boruto's rasengan to engulf Momoshiki's).
Long story short, Momoshiki isn't fodder. He was simply legitimately beaten by two rikudou level ninjas and a kid with a convenient jutsu.