Semantics, but I see your point.
I'll make a hypothetical for you. If Alex Collins rushes for 1,000 yards and 10 TDs, I'll also call that a "career year", because I simply don't think he's very good.
Not exactly the same situation as Benjamin, as I do think he's a low-WR2 or good WR3. But I'm not expecting nor betting on him being a top-15 WR because he's not that talented.
I suppose it would depend on how Collins looks. If he looks bad doing it, your point would make more sense (being skeptical the following season). If he looked good, not so much (assuming it would be a career season). Maybe you would revise your opinion?
Not sure if it is semantics or not, or a case of acknowledging substantive differences and not blurring distinctions.
For instance, Benjamin was a first rounder and unassailably part of one of the greatest WR classes in league history. Collins a fifth rounder in a not particularly exceptional class (after Elliot). They aren't really comparable prospects.
Rookie 1,000-yard rushers in the past two decades through 2014 (31 - add at least Jeremy Hill and Gurley since then).
https://fantasyindex.com/2014/03/10/factoid/rookie-1000-yard-rushers
Rookie WR counterparts were far more rare (see above - closer to a dozen in the past two decades). I just can't think of a single instance where a WR was coming off a 1,000 yard season and was commonly viewed as "not that talented". Even Michael Clayton would have been fine if he could have maintained his rookie level, don't know if he got hurt, fat, lazy, complacent, but he never again looked like the same guy. Benjamin looks like EXACTLY the same guy. WRs can succeed in different ways. He isn't as fast, skilled a route runner and polished a technician as Cooper, but than again, the play where KB just shrugged off the DB like an annoying pest and got some RAC was beast-like. That IS a kind of talent.
But perhaps we are nitpicking. You see him as a low end WR2. The difference between that and a high end WR2, as noted, could be slightly more than 1 PPG. So you have no trouble projecting him for slightly more than 1 PPG less than he would need to be a WR1. To me, that is far from an insurmountable gap.
The main point of disagreement for me is stating that others were extrapolating from one game, when he is merely picking up where he left off. Also, that we should basically pretend his rookie season didn't happen just because they have added a few players (though also subtracting some, like DeAngelo, and Newton's favorite receiving weapon may be Greg Olsen, who was already there and accounted for in target distribution). The supporting cast and surrounding talent is different, but Funchess was nowhere close to as successful or productive as KB in HIS rookie season, so every reason to think KB is going to impact Funchess negatively more than vice verce. Same with Ginn, may not be a coincidence that he put up big numbers in KB's absence. If the overall offense is improved, and they reach the red zone more often (than in 2014), who is more likely to be the beneficiary, KB or Ginn?