The damage difference is more than you're making it out to be - monks and rogues are pretty much on a par at this point in progression for group DPS while rangers end up a peg or two down with warriors. Monks can also take damage much better, pull in pretty much any situation (though rangers are quite handy for that in outdoor zones as well), and due to a number of factors like twinking tendencies, ease-of-epic, and the weapon balance during Kunark in general the average monk tends to be better equipped for damage dealing than the average ranger at pretty much all levels of play.
It doesn't help rangers that many people don't realize that Iksar monks have a higher penalty than the average hybrid. However, hybrids are partially at fault for this. Rangers, paladins, and bards sometimes still bitch to me about how bad they have it for leveling and often don't believe me when I tell them that Iksar monks have it worse (not to mention the fatty and iksar SKs out there). Maybe it's because you don't really hear any of them complaining about how terrible leveling is for them, while every time you turn around there's another hybrid complaining about that 40%?
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I agree with your overall point though. Rangers do get a bad rep and can bring a lot more to groups than many people realize. I really don't think you'll be able to change 13 years of DT fodder and "ranger gate" jokes at this point (the stigma that Falkun mentioned), but I do think individual rangers can and have been able to make themselves stand out as excellent group and guildmates by making good use of their utility skills - but that's up to you to do in game.