I'll be honest, every class is currently "viable" for ranked pvp. Some classes (cough witch cough) just take more skill to pilot than others. Musket is arguably in the "top tier" with an overwatch 5 build utilizing Scratch (mojo echo 3, improved mojo blast 3, witch hunter), Chantal (overwatch 3, burst 2, double tap 2), and Contessa (riposte 2, first strike 3). Even without an overwatch 5 build, musket is still an incredibly strong class. Make sure you have 2-3 Valor's Fortress/Levy's Call/Kraken's Lament and 1-2 Valor's Armor to protect your pirate, a few heals (one revive from gear, pet rally, trained rouse), and a piece of tower gear (Ideally the one giving bombs and a super strike). For pet grants, make sure you have at minimum, the aforementioned rally and kraken's lament, overwatch, burst fire, and scent 2. If you continue to struggle with that setup, ask some of the musketeers in the brawling hall with good setups. There should be some that are more than willing to help you. In addition, it's very early in the season and a lot of the "tryhard" players are still at relatively low ranks. In a week or two these players should be higher, and you'll be able to fight enemies closer to your experience level.