I agree. They were my three surprise cuts, especially considering keeping both Thompson and Frazier (one or the other would have been fine for special teams) and going heavy on the offensive line with both Knight and Redmond (whom I thought got pushed around too much). Thompson, Knight and Redmond would have been my cuts instead.
I also would have kept Phillips over March.
Thompson is the backup FS and Frazier the backup SS while Wilson is injured. I think Heath had some type of injury issue. I think Thompson is ahead of Frazier.
CJ Goodwin is an interesting choice to keep. I thought they would cut him then re-sign him after moving some players to IR-return-eligible.
Players like LB Phillips would not be ready to play now if needed. He flashed but his many missed assignments were less obvious. March probably knows all 3 LB positions. Only keeping 6 with 1 being injured does leave much depth for a developmental guy.
It seems that they might want to trade an OL for a player not necessarily a draft pick. They might want a TE or RB. The injury status of Jarwin/Schultz is a key issue.
Other teams probably wanted to see which players they could claim before those teams consider trading for a Cowboys OL.
Their approach to cuts is different this year. I feel that the team studied which players they thought other teams would claim in part by probing teams with regards to trades and which low level.players those teams would want in return. Some teams must have expressed interest in some OL.