Maybe you're right... for those of us who watch nightly, we often see relievers used more frequently on a weekly basis, thus giving the perception of guys more hot and cold in the regency role. There are also other factors that have to affect bullpen performance that include, but aren't limited to, high stress situations, inherited runners, umpire adjustments to different deliveries, the ability to loosen up after sitting for hours in various weather, and when/if stimulants/opioids have kicked in.
However, when a starter has a "bad" year, it's usually due to a nagging injury or radical change like banning the sticky stuff.