Which one?

[Phoenix]

There are certainly gaps on FMP - transcripts only, rather than images etc.
It is hopelessly out of date, but the National Index of Parish Registers would indicate what was available twenty years ago and show where gaps might lie.
Devon was one of the counties were the Mormons were not allowed a toe-hold and virtually all the stuff on Family Search was from transcripts held by the West Country Studies Library in Exeter.