But that tool you speak of is not needed at all to do older content. I mean, everybody wants gear to pubstomp older content, it's pretty much the entire reason for getting it (getting better gear helps beat current content easier and further trivializes older content).
Again, none of it's necessary so why do you need it? And if you want it, why not wait until the content you want to clear is trivialized? Otherwise, you'll always want BiS gear with every patch/expansion to do old content which brings me back to why I believe it's FOMO. I like soloing old raids. You know what would make that easier? Waiting until the next expansion comes out that trivializes the content via levels and uncommon/rare gear.
My question is, knowing this is a solution that already exists, why do you need the current BiS (now or in the future) to clear older content if current content does not tickle your fancy in the same manner?