Couple of thoughts to add. First, as we all know, the "ground effect" for the Cessna is limited compared, for example to a PA28. Second, everyone seems happy to be running around in warm weather clothes, so the climb performance would have been further degraded in the heat.
In any event, it is impossible to say from the video if the aircraft was over / wrongly loaded. What can be said is the idiots at the end of the r/w prevented the pilot from using the full length.
So, to add to the adage that there is nothing more useless than r/w behind you on landing / take-off, it is r/w in front that has arseholes on it.
My only critisism at this stage would be that he did not check his speed on the roll. And if he did, he ignored rather important data that could have saved lives.
The Wombat
I have just watched this again and even more annoying than the idiots at the end of the r/w is that there was a VERY considerable clearway beyond.