Seriously, people are just looking for something to complain about. So what if they did reuse the basic map and expanded on it? And guess what? They also reused their graphics engine. They also reused the skinning animations (from Far Cry 3 through Far Cry 4 through Primal even!). And I bet they reused a lot of models (animals) as well, and textures, and sounds, and etc. etc. So what? And just look at those maps: it's clear that, while there are similarities, it's been completely redone. Just look at all the elevations (mountain ranges are completely different) or the islands in the river, you can see it's a complete remodel right there. Apart from the general layout, nothing is the same.
I'm all in favor of putting a publisher/dev to shame if they pull something shady, but this is not it.
And statements like "made it a little smaller and then modified it a bit, in hope that we would not notice what is going on" are wild-guessing at the least and clickbait at the most.