Assuming Heath is "below average" (and I would rate him as average) that's still not, as I rate players, "terrible".
There are too many posters who rate players as great or terrible, no middle ground (not you, please note). There are levels of players in the NFL, just tired of the all or nothing comments.
No team can have top notch players at every position, if a team keeps trying to get rid of a serviceable player in the hopes the next guy will be great constantly, you run the very real risk of finding out the new guy isn't what the team was expecting. I really think Heath, as noted, is "serviceable" and the team has bigger needs that will eat up the salary cap, such as OT, DT and (depending on what happens with Lawrence) DE. Just not enough money to go around, everybody has their opinion as to the biggest need, which is fine, we can do that because we're not responsible for staffing an entire team. Heath may well be starting because Stephen, etc. want to focus on other positions...