It will primarily affect the mages for sure.
Lower level mages will have zero chance of survival if being attacked by many players.
Higher level mages that have previously already been going without manashield will not be as affected.
A result in the market might be that Stoneskins and Might Rings etc. will skyrocket in price. They became about 4x more expensive after Soul War Quest was released on some servers, so they might go even higher now.