I agree that waiting for gate is more common now, but overall Alaska's operations have been really good lately. Possibly the early arrivals are the result of scheduled padding intended for bad weather that has not been occurring. At airports where AS has a small number of flights, they obviously share gates with other carriers. However, even at SEA and PDX, it can be an issue because AS has high gate utilization. Still, Alaska's January 2018 operations were very impressive, by far the best of any North American carrier.
89.8% of mainline AS flights arrived within 14 minutes of schedule and 89.0% of total network operations (including Skywest and Horizon branded regional flights). By comparison, only 82.9% of Delta network flights were on-time. Horizon was also the top-ranked regional carrier for on-time performance (even ahead of Hawaiian!)
Certainly, it's only one month, and AS probably had less exposure to bad weather, but it's a sign things are on the right track.
https://www.flightstats.com/v2/month...ports/airlines