Console player here, so no Beta for me. I would think it better to hear any criticism sooner rather than later. I see the difference @saltypatra was trying to make between constructive and purely negative criticism, but again, the criticism will come regardless. At least hearing it voiced in the Beta the team can anticipate a response ahead of release.
And furthermore, the criticism might even be lessened, because certain voices if prohibited from participating in the Beta might feel excluded and incensed that they were not deemed worthy by the powers that be.
Their game, their rules. I took an 8 month break once because I didn’t like the bright green click buttons following a ui update. Some Switch players are on break following a GW update that wasn’t noticed during Beta. Good luck future testers. Have fun. I hope your voices and concerns are listened to and acted upon.