For the most part, my experience has been the mass market lines have had to do a balance of service to price, and service has always lost. We started cruising in 94, and were all Princess, until they started slipping in the service areas, then freefalling. Not sure what the reason was, probably a combination of the brand consolidation, the lower costs, and the tipping policy.
I firmly believe there was a huge difference when automatic tipping came into play (and open seating and alternative eating places). Nobody had to provide you decent service anymore, as their tips for the most part no longer depended on it. They knew most of the passengers would accept the daily charge, and some would give more, so they could work way less and probably get the same, if not more then they did by busting their ....
Price drops, people who expect less cruise, people who expect less leave the same tips, workers deliver less, and the cycle starts. People who expect more go to a higher quality line, and more people who expect less come because they lowered the rates to get the ships full.
You can count us in the people who moved on from Princess, indeed it was a few years where we did not get on a major line (river cruises filled the void, where you know up front what you are getting), until one of our wine clubs did a week long party on HAL last January.