My biggest gripe with 8th & I is that they're generally a bunch of boots who haven't served in the fleet, being led by Corporals and Sergeants who have never served any time in the fleet.
I can't speak for your personal experience working with 8th & I Marines, but I was stationed there, and have a mildly different view.
First off, you have to be 0-3 to even get there- at least the Guard detachment and the marchers, if I'm not mistaken. Mess, grounds, the S shops I imagine consisted of whatever admin MOS was needed, but the rest of us were mostly fresh SOI grads (or if they were guard, they first went to MCSFTCo, Chesapeake, and got their asses shot up with paintballs from FAST Co.).
Second, the men I served with there were some of the most squared away of my whole time in service.
The selection process to get to serve in most of the billets at 8th & I wasn't just about having a squeaky clean background. They had to have 1st class PFT's and top GT scores, etc. Shitbags squeeked in occasionally, but were sifted out pretty quick. Guard detachment needed to be qual'd as rifle & pistol experts.
As for them being boots, etc., some were and some weren't, I'd have to agree. Since 75% of 8th & I Marines are LCPL or below, I'd say they would be boots whether they were in the fleet or not.
This is one instance where we were grateful that the Corps has the doctrine of rotating experienced men in and out of different commands. For those 30 LCPLS and PFC's in one unit with zero fleet time, there were those two CPL's and SGT's with hash marks that could keep them locked on regarding infantry skills. There were also Staff NCO's and officers from diverse backgrounds that contributed to maintaining basic combat skills, PT, etc. If nothing else, when a Marine from 8th & I rotated to the fleet, he was a PT stud, could shoot straight, and was squared away, ready to be molded by the NCO's that took him in.
As for picking them for photo ops, there is a reason they call 8th & I "The Showplace of the Corps".