This has happened so many times. Belichick's policy is clear. If a player isn't good enough to be on our 53, then we wish the player well on another team's 53. The obvious exceptions are injured players, and players drafted in the first four rounds.
I'm sure you all have a long list of UDFA's that we drafted and then went on to be stars for another team. So what. The patriots don't keep players, especially marginal ones, to precent him from having a career elsewhere.
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Also, we IMO, we shouldn't carry 6 WR's (not counting Slater). We carry four WR's. The 5th has almost not reps at WR; he is the PR, if we even have a 5th. Last year Gunner was the fifth receiver. There were lots of WR injuries and we had no TE's. Surely, Gunner should have had lots of receptions. Did he? [Answer: Gunner had 2 receptions]
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BOTTOM LINE
1) The 4th and 5th WR's have very few receptions.
2) We only need a 5th WR if he is a returner.
3) If there are injuries, the 4th WR will might some reps. More likely, there will be more receptions for the RB's and TE's.
4) If there are a couple of injuries, a player will be brought up for the PS, acquired in trade, or a free agent will be signed.
5) I'm OK carrying a 5th WR, given the injuries in 2019, and the inexperience of Harry and Meyers.