Gresham is underrated, imo.
I have no idea if the back surgery slows him down.
But he is a 2 X Pro Bowler. He is one one of just three TEs to have 50 receptions in his first three seasons in league history, along with Mike Ditka and Keith Jackson. If he hadn't missed by 4 receptions in 2013 (and he missed two games), he would be on a current streak of first five seasons). He was a First-team All-American, and has first round pedigree (1.21). Just 27 in 2015. He could have serious upside in NO.
That's all true, but did you watch much of him in CIN? He was ungainly, had some trouble with drops, and though he was tough after the catch he's a lumbering runner. He's just not what I would expect the Saints to look for to replace Graham. Hill is already a poor man's version of the player who excelled in that role.
I agree with some of the above, which you already answered.
If healthy: probably more well rounded, better football player, better blocker and underrated after the catch.
I don't watch all 32 teams every week, but I've seen Gresham enough over the years to sense that I'm probably higher on him than you (I see him as being more athletic than you are describing). Your take may in fact be the consensus, in thinking he is ordinary, I've heard Bloom descibe him a year or two ago with less than lavish praise, so I may be in the minority. He is still available, which doesn't get checked off the positive side of the ledger for him, but maybe that is due to the recent back surgery (teams taking a wait and see approach?). Incidentally, I hadn't read your first post when I wrote mine, but saw it after (not that it would have changed anything I wrote). My feeling, though, is in calling him not good and the definition of average, we are left with trying to explain why his resume indicates a good, better than average body of work. Aside from the two Pro Bowls, it gets my attention when a player has done something few others in league history have. The only other TEs that had three straight 50+ seasons to start their career (and again, if not for two missed games in 2013, it is very likely five straight) were Ditka and Keth Jackson, and I think we can agree they were unambiguously good TEs*. So if it were something any old average TE could do, imo, it would have been done more often. But it hasn't. So I conclude, sort of on the basis of a modified extension of the Sherlock Holmes process of elimination maxim - if you have eliminated attempts to explain away that the achievement was special (speaking of myself, and I can't find any reasons, good or otherwise, to explain it away), maybe he is better than average and underrated.
To put it a different way, if you had been on Mars the past half decade with no Sunday ticket, and knew nothing about Gresham but that he was a 2 X Pro Bowler and shared the distinction with Ditka and Jackson, would the first thoughts that came immediately to mind be that he must not be good and was the definition of average? Based on that, I'd be inclined to think he was pretty good. Another fact that could be interpreted a few ways, is that he was on the same team with Green (NFL record for most receptions through first 2-3 seasons, at least). On the one hand, you could say Green was drawing coverage and Gresham was never double teamed. On the other, there were a lot of receptions that went to Green, that on a different team, might have gone to him in different circumstances?
Drop rate is an interesting point, because Graham had some drops himself. Lumbering is subjective, he isn't T-Gon, Graham, Gronk, but I think he can produce better than average numbers in the right system.
Hill is a player I haven't seen play enough to speak to (unlike Gresham), so I'm at a disadvantage in making the comparison you are. As noted, just speaking to Gresham. My sense, there is only one Graham, so how poor a version is he? If he is a completely destitute man's version, or dim reflection not really remotely like him, than NO may just look to put the best TE out there, even if it ends up being a different skill set. Which you already alluded to, so I agree with that possibility you threw out, that makes sense to me.
* TEs with 50+ receptions in first three seasons club
Ditka - 5 X Pro Bowl, 5 X All-Pro, he actually also had 75 receptions in season four (only TE with 50+ receptions in his first four straight seasons, though I think he never came close to 50 again?).
Jackson - 5 X Pro Bowl, 3 X All-Pro (just missed with 48 receptions in seasons four and five).
** Video highlights
Gresham at Oklahoma ('08, admittedly a while ago, but he is just 26 - turns 27 later this year - that year Oklahoma had a prolific offense, and he was the best receiving weapon on that team)
https://www.youtube.com/watch?v=DLXZq7Rv_NY
CIN ('12, the plays at 1:15 [[shown again from a different angle at 1:30]] and 3:25, I wouldn't characterize as lumbering, the catch at 1:55, and especially the one handed ones at 2:20 and 3:00 are pretty athletic, the play at 2:35 in which he drags 3-4 Chiefs into the end zone for a score flashes power, balance, toughness and determination)
https://www.youtube.com/watch?v=_PgXpls_KWA
I'm not sure why the disconnect in what we are seeing. He is a big, strong dude, he isn't Shannon Sharpe-sized, as far as his speed, movement skills, COD, elusiveness, RAC ability. In recent years, did he get bigger? Did the herniated disc cause his play to deteriorate in the past season or two? Was it a scheme and coaching decision to send him almost exclusively on short/intermediate routes. Could he get more route depth on a different team, with a different scheme and coaches?
Dunno?