Tch! Swampert is by far from weak, my friends.
Grass Types may pwn it, but take this into consideration:
Decent stats, STABed EQ and Muddywater/Surf, put Ice Beam on him so he pwns the grasses, and finally do Endeavor in case you're low on HP.
Or you could replace endeavor with Mirrror Coat, reflect all that damage done by grass type attacks.
So, Swampert totally owns if you give it the right MS and EV train it properly.