I joined easyJet with 7500 hours as an FO, at a time they were desperate for commanders and there were no waiting lists - and it still took 18 months to run through the process to command.
easyJet have no seniority - true, but it is a one type airline (no need for seniority for fleet bids). Once a person has completed command assessment they are on the list, in position, for promotion - and that list is currently 2-3 years long.
Having said that - it is a good airline to work for, with good people.