If you're talking about confluxes 1 and 3, which are the easiest confluxes and the only ones most in which most soloers can effectively operate, well, you basically took his mobs and have zero sympathy from me when you could have just gone to a different flux.

And you're almost certainly talking about 1 and 3, because you're complaining that people do this to you.
Most annoying leech we ever had was on our first (and last) attempt at flux 5. We were kiting the boss because we were having difficulties. Guess what our difficulties were? An idiot rdm with a joyeuse feeding the thing wayyyyyy too much TP and not taking hate because he was hardly doing damage. This idiot rdm kept chasing it around while we were kiting, smacking it with his trusty joyeuse. Guess who got one of the 5 finishing chests even though there were over 18 people in there? That's right, the leech.

But yeah, you're right. I'm betting that rdm was just going in there to solo when our group popped out of nowhere and ruined his plans.

That was our last WoE run we ever did because we were sick and tired of feeding loot to people who deserved nothing short of a kick in the pants. People threatened to leave the linkshell if we kept doing that crappily made event.