The Broncos came from 34-4 down in the second half to move within touching distance of a draw, a comeback that pleased coach Rea.
"We had a really good attitude to do what we did in the second half, it was very, very hot out there, and that possibly affected our concentration at the start of the game but that would be an excuse and that wouldn't be acceptable," Rea told Sky Sports News.
"A team without any character would have rolled over, and we showed in the second half, the most important thing we need to do is to show that character from the off and get ourselves into the arm wrestle.
"There are two ways to look at it, one that there is enough fight and talent out there and they are showing that but on the other hand, the starting part of the game is clearly an issue for us. Our intent was really good, our preparation was really good, just defensively they managed to wriggle out of too many situations for mine and our liking."
The Londoners remain bottom of the Super League table following the defeat.