Then those QBs were serviceable for the season in which they took their teams to the playoffs.
In 2005, Chris Simms had a QB rating of 81.4. Not "horrible" in the least.
In 2003, Kyle Boller had a QB rating of 62.4 as a rookie, but the Ravens were NOT on pace to make the playoffs until Anthony Wright took over. Wright led the Ravens to wins in 5 of his 7 starts, and had a mediocre QB rating of 72.3.
In 2002, Tim Couch's QB rating was 76.8. Mediocre, but not horrible. One might say it's *gasp* "serviceable"!
In 2001, Elvis Grbac's QB rating was 71.1, which is surely mediocre but not quite "horrible".
I guess it depends on your definition of "horrible". To me, Quincy was mediocre but "horrible" is a bit of a stretch.