Two things before I start :
1- I know FIFA’s ranking is nowhere near perfect.
2- It’s well known that averaging reduces random errors, so this should give at least a rough picture.

8 - Group A :

Russia (65), Saudi Arabia (63), Egypt (31), Uruguay (21)
Average Ranking : 45
Average Ranking w/o Top Team : 53 (8th)

7 - Group G :

Belgium (5), Panama (56), Tunisia (27), England (15)
Average ranking : 25.75
Average Ranking w/o Top Team : 32.67 (7th)

6 - Group H :

Poland (7), Senegal (23), Colombia (13), Japan (55)
Average Ranking : 24.5
Average Ranking w/o Top Team : 30.33 (5th)

5 - Group F :

Germany (1), Mexico (16), Sweden (18), South Korea (59)
Average Ranking : 23.5
Average Ranking w/o Top Team : 31 (6th)

4 - Group D :

Argentina (4), Iceland (22), Croatia (17), Nigeria (50)
Average Ranking : 23.25
Average Ranking w/o Top Team : 29.67 (4th)

3 - Group B :

Portugal (3), Spain (6), Morocco (40), Iran (32)
Average Ranking : 20.25
Average Ranking w/o Top Team : 26 (3rd)

2 - Group E :

Brazil (2), Switzerland (, Costa Rica (26), Serbia (37)
Average : 18.25
Average Ranking w/o Top Team : 23.67 (2nd)

1 - Group C :

France (9), Australia (39), Peru (11), Denmark (12)
Average Ranking : 17.75
Average Ranking w/o Top Team : 20.66 (1st)

Three Quick Takeaways :

1- Group A is definitely ‘The group of life”, if there is such a thing. It’s clearly easier than all other groups.

2- The other groups are rather close, as you can see from the numbers above, especially given the faultiness in FIFA’s ranking. Of course, some groups are stronger than others but, there is no clear “group of death”.

3- Spain vs Portugal is definitely the match to look forward to, considering ranking or not (At 5, it has the highest average ranking of any match-up in any group).