There is a finite limit on how much power advantage you can gain via *ing, which can be overcome with skill or number(in case of battleground)

The amount of power difference that can exist in this game thou....

There is also the matter of rewards. In WoW, *s does not stop other players from getting the rewards. It might be harder, but it doesn't prevent it. Also, most of the rewards at a given level bracket only applies to that bracket, some currency can be carried forward but there is a finite limit of how much. For a non-*ing player, generally speaking they don't care much about those rewards, as they would become obsolete as they level up anyway. Not so with this game, the rewards in sage is universally useful and therefore losing out on them due to * is a permanent material loss.

Therefore, WoW * is not equitable in both the scope of "harm" and the seriousness of the actual "harm"

That said, I do not blame the players, only the way the sage is structured.

#2, yes
#1... there is really no need nor does it help. Thing is, you will initiate a level up as soon as you gain ANY exp. And there are a lot of things that even the level suppressors would do that grants exp. This includes ninja exam and groupy summon as well as, of course, doing any instance. The real way people slow level is to not do high exp income stuff to begin with, so opting out fox, daily/weekly missions and ninja test is the way to go. I seriously doubt there are many, if any, players are still holding out on the built up exp. And certainly, none of them would be 88, all of them would be 85.
The best way to force player to level would make daily mission auto receivable, and weekly mission somewhat auto-receivable(up to 3 common and both premium are automatically received) Of course, one can prevent oneself from receiving the weekly one by not completing any by constantly refreshing them between doing different activities, but it would make that much harder.
Unfortunately, we can't really force player to do fox... We could, however, add exp reward to sage itself.