That would seem to make it harder to eliminate the obvious winners that everyone knows they need to vote out which means there will be hope for us when we are rooting for the runaway winner to make it

I'm not sure I follow. Sure it makes it harder to vote someone out at F4, but I think the structure incentivizes everyone to eliminate obvious targets earlier instead of keeping them as shields.

I think the biggest plus is that it's harder for threesomes to steamroll their way to the end once they're at the F6. Think Kim-Chelsea-Sabrina or Tyson-Monica-Gervase* threesomes. Now such threesomes will have to contend with the question of "well if Tyson wins final immunity, will he take Monica or Gervase?" Such structure would make it more likely that the Monica or Sabrina player (that is the clear third of the threesome) will flip.

We definitely want suspense during the finale, and if there's a strong threesome at the finale/F6, it's not going to be as exciting.

* (without someone as strong as Hayden in the mix)

imo, it makes challenge threats an even bigger target post-merge.

you dont want to be drawing dead in the final 4 immunity

This is with the assumption the players are smart enough to even consider this. Unfortunately, most seasons dont have players who even consider these things. So I guess it helps the few strategic players who are even capable of using this to their advantage.