They have stiff competition with some of their previous incarnations, but with 19 starting rookies, yes they are historically BAD. YOU need to just wake the fuck up and stop inventing stupid shit just in defense of Dez. You're actually saying the 0-9 Cleveland Browns who are stinking it up again right now on national television, aren't the worst NFL team in 30 years. If you think they're not, then by all means name the worst one.
There's probably several. For starters, the Browns might not even be the worst team THIS season. The Niners are certainly as bad, if not worse. Right now, the Browns have a point differential of -105 pts in 9 losses. That's bad, but its not catastrophic bad. That's a little under 12 pts per game. The 1989 1-15 Dallas team was 1-15 with a point differential of -189 and scored only 204 pts. That's also really bad, but not as bad as some other teams.
The 2008 and 2009 Lions teams were historically bad. 0-16 in 08 with a pt differential of -249 pts. In 09 they were 2-14 and had a point differential of -232 pts for 16 games. They gave up over 500 pts in 08.
1990 New England was also historically bad. -265 point differential and scored only 181 pts for the season. That's barely 11 pts per game.
1991 Indianapolis was 1-15, had a point differential of -238 and scored a paltry 143 points. That's not even 9 points a game. They might be the worst team ever.
I'm sure there's a few others but could do more research. Cleveland this year might go winless and ultimately could end up worse than some of these, but I think its doubtful.