There are more A321 deliveries next year than 737s. This year there was supposed to be more 737 deliveries. At my seniority of 5 years every base that has both planes I’d be more senior in the 737.
I’m not sure if we kept 737 staffing up for the planes we have parked/awaiting delivery or if the 737 staffing slipped to what we currently need.
I think you’d get faster seniority progression in the airbus because of the deliveries in 2020 but the 737 shouldn’t be far behind.