I think SE are completely oblivious to the part where people are gear swapping and have been for most of the game's existence. Item Levels just don't work for this reason, your level taking into account the gear you use is going to go up and down like a yo-yo due to this, the only piece of applicable equipment that melee's would use fulltime in these situations would be the weapon.
In addition to this, the item levels for melee gear have far surpassed that of other jobs (WHM, GEO, SMN I can see being examples). In relation to Summoner, the only relevant pieces of gear that they've added for the job since Adoulin's release are weapons, Bokwus Circlet, and Bokwus/Orvail Body.
In terms of melee gear, for some jobs (like SAM), there's minimal TP gear from Adoulin that is considered optimal, making your "Item Level" if you defeat the mob whilst in TP gear lower than when you defeat it in weapon skill gear (In terms of SAM, only the hand equipment from Adoulin is in any way the best piece in that slot at the moment barring weapons, the rest is beaten by AF3+2/Usu+1/Phorcys).