There's still a number of unlocked nodes near the edges of the cantina, so I'm sure there are more features that haven't arrived yet.
As for the teams with 4* leaders in top ten, I would wager that the rest of their team is very strong. There just happens to be some unfarmable characters with very good leader skills, which is why they're using them like that.
Being at or around rank 50 as a free player only 2 weeks in is actually very good in my opinion. You're doing pretty darn well so far, congrats.
They're also in different "arenas" based off of when they downloaded and started playing. Mine is about a month old and we just got our first 2 lvl 60's. A couple ppl have 6* sids as leaders but most are 4 star bariss. I expect it to continue to change as other heroes get starred up etc
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As for the teams with 4* leaders in top ten, I would wager that the rest of their team is very strong. There just happens to be some unfarmable characters with very good leader skills, which is why they're using them like that.
Being at or around rank 50 as a free player only 2 weeks in is actually very good in my opinion. You're doing pretty darn well so far, congrats.