if it takes 20 faction terminal missions to gain a level, then it may be that the xp gain is offset by the faction gains, as i levelled from 80 - 90 by doing 10 terminal missions a day, and getting a level every day, with the exception of levels 89 and 90, they generally took 12 - 14 terminal missions. on the up side, at level 18 i was getting 2 levels just from the terminal missions, still not all that drastic a difference even so, its a personal preference i guess. with the decider being whether you want faction points at all.