Any argument for a WR that has to start with "irrespective of his catching" is, at best, starting with an enormous caveat. More reasonably, it's just generally missing the point of wide receivers.
Yes, he's moderately faster than LaFell. Not a ton faster, I think people here place too much stock in his pro day 40 time, ignoring that pro day times are notoriously unreliable. But sure, he is faster, and in exchange he has much worse hands, runs worse routes, runs fewer routes, doesn't attack the ball as well, doesn't use his body as well, and doesn't block as well. Calling Dobson's hands questionable is a polite euphemism from what we've seen over the past 2+ years. A more blunt, honest and correct assessment would be that his hands suck. Also, I think your evaluation really undersells how good LaFell is, because we repeatedly saw LaFell punish defenses with deep completions last year. Plays were he ran great routes, beat his man, used his body to shield the ball from the defender, and actually made the catch.
Dobson's on the field now out of necessity, because until LaFell gets back there's no better option at split end. And in his time on the field, he's shown that he is what we thought he was. He has size, speed, and little else going for him. He occasionally flashes talent with a good week, and then follows it up with what we saw on Sunday. His hands can't be trusted, which means he can't be trusted. A WR with legitimately bad hands is borderline useless, so if he doesn't show that he has passably good hands in the few weeks he has left before LaFell returns, he'll be riding the bench once LaFell gets back.