The version field is useful to specify a default/baseline version to target if the package does not explicitly specify engines field. This is sensible, as these rules are usually pulled from templates or sets of rules targeting a specific node version, but should be overwritten by the specific node version of individual packages.

Having the version field overwrite means that it is not possible to specify a default node version (besides the 8.0.0 default) without then ignoring packages' engines field.