I think there is some truth to that. 10 people that play all the time vs a medium or large guild with a bunch 10 hr a week guys, a few perma deathers that slow crawl lower end content, etc... can show a big disparity in guild achievement.
Guild ships/amenities are fine but I don't think there is any perfect solution. I don't like the whole decay setup, but that is me. I dunno if further tinkering is going to solve anything.