Let's take the current ranking (with points from qualif. and entry points for Season 6). The lowest the sum of rank, the toughest - in theory - the group:

Gr. A: 28
Gr. B: 59
Gr. C: 38
Gr. D: 57

So in theory Gr A, with the defending champion (that's me :-) is the toughest. I should say it is indeed, but not because of the rank - the reason is everyone can do +30k steps and therefore beat everyone else. I bet that none of us will have 6 wins but also non will end with 0. If my rivals read my daily updates, they will know when I am vulnerable :-)

If you look at Gr B and D, the sum of rank is very high. It's due to two novices, who entered with a low rank. So you'd think "easy-peasy".
But in the eliminations they were doing +30k and certainly can repeat that in the group phase. (speaking of @ziabutt3836 and @matthew1 here).

One thing is sure - for all groups: if anyone thinks of finishing in the top 2, they need to average 25k and I would say that any day with < 20k, means a defeat.