It's possible to support your team and be realistic. I would guess that the USA and Mexico deserve to be within the #8-15 spot. Both of them are what I consider a tier2 side (tier1 being Brazil, Italy and whoever else is peaking atm). Tier3 would probably be Costa Rica, then I would put us in the tier4 category. I think we are capable of being a tier3 side, however we don't have results to justify it yet.
CONCACAF is not as strong as UEFA or CONMEBOL. Concacaf has the most nations however the majority are small islands, the actual competitive footballing nations would be perhaps 1/3rd of the total amount. Mexico is perhaps the only real historical large footballing nation in our region. The USA has only emerged as a real power in the last decade. The central american teams have similiar population to some European powerhouses, eg. Guatemala and Holland have similiar populations, Sweden has near Honduras' population.. yet the level of football is about two tiers higher.
The USA versus Mexico is a complex ranking. Head to head, there is no doubt that USA has the advantage. However, Mexico has performed better on the world stage than the USA. That's what makes the whole ranking screwed, the USA has not played any tier1 teams in the last year to justify being considered a tier1 team. In the past 3 years, they've played close games with both tier2 and tier3 teams, and lost to tier1 sides. Mexico faired better with their confedaration's cup run so one can argue in the eyes of the world, Mexico is better. The answer isn't clear cut.