No is not the whole room just a differing of targetted AoE ... he currently uses banish every 30seconds to one minute ... in a high dps (a lot of booted melee) he may get 2 or so banishment off when are less boots on melee maybe 10-15 or so. It's uninteruptable and does not follow our own casting time or cooldowns.
Personally after the change I would be reluctant to take any prime party memeber in without boots. Loss of a cleric, bard or caster and anyone dealing with sally halfway through the end fight in a pug group actually can mean failure of the whole group. Not so much in a Guild run... but the risks still exist.
Thus comes to this... if you wish to run this raid, get boots or tell the group and ask politely if they mind taking someone less then adequate.
My view on this is ... I suspect the random banish targeting was intended in the original design to prolong the quest life of devils-battlefield ... However power gamers are saturated from the raid by now, more interested in the next big raid or area... the casuals may not persue it due to the time consumed and low payback to just gaining boots ... as such this area of the game may become a ghosttown.