I don't think anyone is saying Gibson can't be the guy, just that (like every position on the team) the job can be taken from him.
Collins situation is different because his payroll, but I don't think Rivera would hesitate to shelf him if it's clear that Curl is better for the team.
I also don't think Harmon is getting a pass. The team added 4 WRs this off-season. McLaurin is likely the only one locked into a job at this point. If Collins or Harmon don't produce as needed, then they likely get the hook. The same can be said about Gibson. Not saying he will get cut or dumped, but if Patterson proves he's got the leg up, Gibson role could change. It's a long shot but haven't we always wanted the best player to play regardless of draft status? It may not be likely but it's possible.