It's not an easy task, but if you're having to not go through a lot of the design process because the original exists as one of the greatest games of all time, then that's an incredible amount of help for the dev team. Consider than nearly every member of the 300+ size dev team has probably played FFVII, and at any time they can go to it for reference. A lot of what we see and what's been described is beat-for-beat the same as it was in the original such as the Bombing Run. Of course there are changes, but everyone in the dev team is on the same page and knows what the end result should be like. A lot of what we're seeing is the same FFVII with new things added on to it. The base character designs, personalities, script, enemy variety and designs, themes, etc. are all already established.
It's not going to be a lesser achievement if they pull it off, but it doesn't compare to creating a brand new FF from scratch which they've consistently failed to do for well over a decade now.