That list spans thirty years and WWW was not a Patriots pick. You make my point ...
It doesn't matter that Welker wasn't a Patriots pick. The fact of the matter is that he was a Late Round/UDFA receiver. I forget where I heard it but a couple years back they actually showed that that there were more ALL-PRO players who'd been UDFA than 1st round picks.
There are always late round/UDFA picks who surprise. Every year. Just because they aren't on the Pats doesn't mean your point is made. It just means that you're purposely limiting the pool to push your point.
I have no idea if Douglas and Boutte will succeed as Patriots. The field is stacked against them with Parker, Bourne, Thornton, Nixon, and Bowden on the team. That being said, this is the fewest number of WR I can remember the Patriots bringing into TC in years. Usually its in the 10-12 range.
Douglas brings a skill set that none of the other receivers on the team has. Not even Smith-Schuster. IF (yes, big if) he can learn enough of the playbook and apply what he learns to the field, he's got a very strong chance of making the team because he brings Special Teams play with him. Of Parker, Thornton, Bourne, and Boutte, only Bourne has previous STs play. But the last time he did anything regularly was back in 2020 on the 9ers. Parker, I think, might be on the hands team for On-side kicks, but he's got a whopping 10 snaps total in 8 years.
Tre Nixon didn't work on special teams in College. We have no idea if he's been working on that as maybe a Gunner.
Bowden had college Punt and Kick Return experience, but didn't do that with Miami prior to coming to the Pats. He might offer something as a reserve returner, but we don't know what he might bring at this level.
So, let's not go ruling out the 2 rookies because I don't believe the Pats would have drafted them if they felt they didn't have a shot at making the team.