It's possible to reach that group level, IF everyone donates religiously every day.
Although from what I've experienced, the group that I'm in was only able to reach level 6 before that rewards ended. We were halfway from reaching level 7, but not everyone donated max every day so... yeah.
When my group leader recruited people, first two days he strictly kicked out people who didn't donate. So when the group reached lvl 3-6, only the members that have been there since day 1 stayed and were able to get rewards. He never recruited/accepted anyone, even when the group upgraded into 3+.
It's inevitable to keep people from joining just for rewards, and leech off of the group. That's why it's better to scope out loyal members in your server ;)