Data data data. If you have stats to back up that you can be productive offensively, specifically moreso then your partners, then this is the best way to drive your views on who you think should be playing what roles.
When we talk to our alliance partners before every match, we have a summary of our scouting data on hand for this exact reason. Not only does it help us figure out what strategy we think is best, but helps our teammates understand why we think we should play a certain strategy.
Early on in the season, of course you don’t have any or as much scouting data so this is harder. There’s definitely a lot more trust you just have to put into teams, and whether you like it or not team reputation and prior performance in previous years (especially the last year) will probably influence what other teams on your alliance think everyone should do. The play here if you really don’t want to play defense is lobby for a 3 offense strategy. Obviously every game is different so this is kind of a case by case basis but at early events this year 3 offense strategy made a lot more sense unless you were up against a 1678 or something and defense really was necessary.
Finally, the biggest thing is perspective. Make sure you’re always being really honest with yourself about your capabilities and your offensive potency compared to your partners. It’s really easy to get caught up in what your max cycles per match has been and thinking you can do that every time. If you really are better then your partners, try to have as many hard facts as possible to show that. Also understand if you are not then at the end of the day every team has a responsibility to their alliance to do the best thing possible to win.
Also as an afterthought, smart teams do pay attention to who is willing to play defense and who is not. We had teams who fell way down on our Picklist or was just left off it because during qualifications they were not willing to play defense. Or when asked in the pit they said they were not willing or really preferred not to.