I don't know whether it's a problem or just a reality - but you're right, however the ages are chosen and combined to determine "club strength" is always going to have pros/cons. Here's the full data of all top teams across HB Koge and Surf for all ages from 2014 through 05/04. Koge has a stronger team (by rating) in 2011, 2007, and 05/04. Surf is ahead in all other age groups. HB Koge's top team in 05/04 is so significantly better though, that it dwarfs most of the other differences. Mark's intent for club strength is this (
from here):
View attachment 17673
You can directly see the effect of choosing different populations. In the current setup for the app, the first result, it shows that Surf is slightly ahead. This is close to what I'd expect to see on the app either today or tomorrow. If other populations are chosen instead for the calculation, including the 05/04 age, Koge is slightly ahead. There are 992 clubs in the US with enough active girls teams to be rated as of today, and these two are the very best of the best - and are also quite close.
Those interested could likely lobby Mark to start including the U19s (which will be the 06/05 group on 8/1) in club rank if they feel that it would be a better representation than the current setup. You'd have to ask him, but my hunch is that he leaves the top age group out only because of that 2-year wonkiness and less fidelity about which team is actually which for that age group.