No, I mean human centric as in humans being the almight special/more important/vital to the survival of the universe type of centric.
Its just when writers throw in tibits that make it seem like its ONLY about humans is what drives me crazy. Personally ME2 would have had a greater appeal if it was colonies of all races going missing instead of JUST humans. ME3 would have had a better appeal if the overall them was to take back the home planets of ALL the major species and not JUST Earth. Taking back Earth should have been a normal mission in the same way Palaven's Moon, Thessia, and Tunchunka was. The final mission should have taken place in the fringes of space on some unknown planet/moon.
The problem with colonies of all species going missing is that ALL species would then investigate. There would be no need for Shepard to work with Cerberus, there would be no need for cerberus to really interfere. So collectors would have killed Shepard and thats that. No need to really bring him/her back since the rest of the Council species are as interested in finding who is abducting their colonies.
As for the whole Earth mission, that is true, but it fit in with the whole theme of the game. It starts on Earth, Shepard gets out on the Normandy to find help for Earth. Earth is proportionally the weaker one of the council species and is in under a stronger attack. Its only later when the Citadel gets moved there that instead of just helping Earth the mission becomes of vital galactic importance.
Before that Earth mission was only really vital to the humans.
To change that they should have slightly altered the tone, instead of overwhelming attack they could still have a large scale one but with Reapers also dying. Just because reapers are vulnerable it doesn't mean that they are beatable by conventional means. For example for every reaper dead the fleets might exchange a dozen cruisers, or something like that.
By genetic diversity they didn't mean that we as humans are somehow REALLY different from each other. Its the small things like skin colour, height, muscle mass, proportions, hair colour and texture. For example people of african descent find that some of the medicine for certain heart and other muscle related problems do not work as well on them as on the people of caucasian descent. We simply havent mixed enough genetically to be quite similar to each other.
Turians, salarians and asari however are. Vorcha might also have been genetically diverse but they are not exactly an advanced species, they might have even be spared since they dont have the ability to develop the technology.