The reason for this question is new players like myself cant afford a Seal of Expensive bow yet and must make do with a lvl 18 +4 or +5 bought or made for 1 to 2 million.
Maybe after once or twice going from 18 to 20 and back again then the nice SOM 16+5 can be afforded. Then of course going all the way back to 16 would make the best use of such a weapon.
So, to sum up and rephrase, is the level down that you delevel based more on the weapon you have to use, and if no SOx weapon is available can you grind just as well at 18 instead of 16. Thanks for reading my long and repetative question.
P.S. If a player NEVER intends to go back to 16, he can up his masteries to lvl 9 and max the first imbues/skills available and thus kill mo' betta'