Cobb had a pretty amazing season for a #3. Love the Lamb pick, but Lamb is unlikely to match that kind of production (as far as first downs, and yards relative to targets) unless an injury thrusts him into one of the top 2 starting WR jobs for a good chunk of the season.
This pick hopefully sets us up to have a good receiver corps for years. But you might be kidding yourself if you think it's a day 1 upgrade over last year. Our WR trio is, for right now, a downgrade from last year.
But promoting Jarwin improved the TE position so perhaps our passing game weapons, as a whole, have upgraded.
(And hopefully the passing game weapons are all improved thanks to Kellen Moore hopefully being turned loose from some of the rigidity of the previous regime. Maybe McCarthy helps with his own scheme stuff too, though there's a reason he earned the reputation for having let his offense go stale in his last job, so I'm not holding my breath waiting for McCarthy to be the magical fix by himself.)