iPhoto is no longer developed. Sooner or later a version of the OS will come along and it will no longer run. It won't be this year but it will happen inevitably.
So, yes, it's time to plan for life after iPhoto. But you don't quite have to abandon it yet, and might want to wait while Photos progresses along its development path.
I'm guessing you're referring to the option to Copy Items to the iPhoto (or Photos) Library on import?
By the way, went to Preferences in each of these apps and there is a choice to "import" to that app in
both Photos and iPhotos, if I do not select to import to iPhotos and only to Photos then I believe
that the duplicating imports will stop; am I correct in my reasoning here?
That is not what this means. iPhoto and Photos are quite unaware of each other. If you import a photo to iPhoto, Photos has no knowledge of it and vice versa.
That option refers to managing the files, and it's quite important.
For more on iPhoto and file management see this User Tip:
https://discussions.apple.com/docs/DOC-6361