Heavy offense is a playstyle that uses no walls. There was a thread about it, it got locked but there should be some good info.
So yes, walls are optional.
Personally I don't think offensive teams should have any old walls, but rather what I call 'supporters'. Screens, wish, baton pass + boost, statusing the enemy, etc. These Pokemon will often have a degree of ability to stall on their own, and they can be the same Pokemon you'll see on balanced or stall teams, but their main purpose is to help the offensive mons, and their movesets should reflect that.