You will indeed need all the assault weapons you're able to get on the long run, just factor that for the End-Game you want to have a full SSR Mono Grid for all attributes, also personally I try to recommend to everyone to stop neglecting Defender weapons; especially if you want to be able to complete the most difficult content this game has to offer; remember that, yes having full assault is cool and all but when you have an Eidolon that only provides Attribute ATK you might be lacking quite a bit of HP to live through Overdrive Blasts, in no way shape or form I recommend you should focus on defender weapons but for me 2-3 Defenders and 8-7 Assault weapons make a perfect ratio in the long run...