Yeah. He was in his full right to say that. Maylene, as far as she showed her skill vs Paul, was about as skilled as a baby saying "gaga". You can say it was mean, but I'm a rather nice guy and I'd probably say something like... "Wow, that sure was easy compared to the other gym leaders..." anyway!
Not that it makes any sense in regards to the game though. Roark is not wanted to become a gym leader and only gets the spot because the guy wanted for the position turned it down... and when defeated he says he's by far the weakest Gym leader in Sinnoh.
Meanwhile, Maylene in the games was so strong that she got promoted to her position without realising it.
But meh, I'm nitpicking. And Maylene's awesome. Perhaps she's far from the best trainer in the series, but she could kick Paul butt in a fight(lol, kicking aura spheres around, getting blown up by aura spheres when not prepared and takes less damage than our dear Rockets).
*Starts shipping PaulxMaylene for no reason other than that she can beat him silly*