It would be great if default values for all options in the "Transfers" section (e.g. "Source files", "Exec command") could be provided in the global configuration in a way that would reduce each job's configuration to selecting the server.

I guess it's a common use case to use Jenkins variables like ${JOB_NAME}, and this makes the configuration much the same - save an occasional exception for a legacy project. To reduce duplication of config data, it would be nice to set some defaults for each configured SSH Server and then be able to overwrite them occasionally, but if nothing is configured explicitly the defaults from the SSH Server configuration would be taken.