In the races they've both finished Hulkenberg leads Perez 5-3 and Perez got Force India's best result of the season. Considering he was ditched by McLaren after just one season and that Hulkenberg is regarded as one of the best drivers on the grid I don't think you can point hte finger at him as someone who is struggling with the new regulations.
As for Grosjean, Maldonado might be a crap benchmark but that Lotus is a disaster of a car and I doubt anyone on the grid could make driving that thing look pretty.
Button leads Magnussen 8-2 in the races they've both finished, what else can he do? Magnussen may be a rookie but he's a highly rated one.
I just don't think those three are struggling compared to how you'd expect them to be performing.