"everything would've been the same"

The lack of copyleft makes a difference. We don't have a time machine to go find out how profound the difference is, but it's clearly _some_ difference.

There have also been very important cultural differences. Again you could say that in the absence of Linux maybe there would have been cultural changes in FreeBSD but that would be pure speculation. Historically the BSDs have suffered schism, not once but several times, and the same hasn't happened to Linux. Is it just one man making that difference?

Very fundamentally, Linux is a kernel and the BSDs pride themselves on building whole operating systems. Whether that's a good thing or a bad thing doesn't matter for this purpose - it's a mammoth difference.