This is not an exploit because the person was in your guild and they joined the guild war party. Limiting your members to being high ranked and strong to the party only is a fast track to having people not want to be in your guild. This was just a person being a bad sport.
Funded Elves are the strongest race at the moment, it's just that you guys don't have an understanding of the end game. You're probably thinking about elves without funding. Elves have the fastest clear rates through out the board on relevant content like phantasm, sidhe (mostly boss), aahm ,rahm, cahm.
What are you even saying? Mag hits 150-200k+ crits on 0.5s cooldown, crash shots hit over 150k on main target w/ sufficient target count and 40k+ on fragments, and they also have vision for the aim buff...
You forgot to mention that you have to drop a lot of money, which most people don't want to.
If the players who made these elf fast-clear videos put the amount of money they invested to be able to "fast-clear" in their video descriptions, no one would even bother playing as an elf to reach that so called "end-game" (unless your priority in life is a mess)
The secret to 150-200k mag crits is really the magnum combo cards which requires real life dollars to renew. The glove reforges and the behomian set which is pretty cheap help too but the major factor is the combo card. The weapon you'll be using itself has huge diminishing returns as you upgrade to better and better weapons.