There is nothing wrong with your strategy per se. That said, you did just miss the increased sign-up bonus of 75K.
Historically, Chase & Southwest offer an increased sign-up bonus for Southwest credit cards right between October and early December: Discussion of Chase RR Visa 40K-75K sigunup points offers -- NO REFERRALS! - Page 301 - FlyerTalk Forums

Many of us sign-up for these increased offers during November, spend most of the way through the holiday season - but holding back from getting the bonus until Jan 1st.
When timed properly, you could get the Companion Pass for almost 2 full years.