Yes S rank launcher is the best s rank for ranger
Of one-hit hell weapons, the best would be yas7k, he has 5 more ata than asteron and I personally love his firing animation
Also Arrest faust is better than frozen, for the simple fact that frozen cannot be accumulated, but arrest yes, if you basically don't understand when you hit special arrest, the effect is reset, but with blizzard that doesn't happen, you have to wait for the effect to wear off so you can use it again.
Yas9k gush with df? I didn't understand that here bro, yas9 is only for rangers and df is only for hunter, but anyway yask9 gush is a "fun" option to use, at least I wouldn't use it, it would be to have something else in the inventory that it will occupy space. A ranger literally only needs Dark meteor, effect weapons like arrest/blizzard and impact weapons like demon/hell, a basic set would be dark meteor+frozen shooter+yas9k demon and with that you can do quite well if you are looking for something cheap. The ranger's job is to impact the game, deal damage and always keep his distance