It depends on the map and how bad the players involved are.
I'd say shock-rifle tertiary fire is "unfair" because it takes very little technical skill to use it well, but I can understand why it's still in the game and whatnot.
I'd also say that on very tight maps, grenades can be very powerful (see: battlefield series), which can seem quite unfair if you spawn and instantly die.
Most weapons have some weakness, or something they're bad at which another weapon is better at...Simply exploit that. Many strategies have counter-strategies, including camping, using the SUPER IMBA GUN, and 'nade spamming.