Side comment for emphasis:
Foresight is a 9th level spell - that is, the highest possible echelon of magical casting, that contains spells like meteor swarm and wish. It's available to 17th level pure casters that have dedicated their entire adventuring career to gaining this degree of magical ability.
Foresight's purpose is to give one target free advantage all the time for 8 hours.
So well spotted.
I like this idea (also expressed by others) : if we look more broadly that my post, which was strictly about the inner-working and the numbers-output of Advantage, and we look at the cost of getting Advantage, what is comparable to what ?
- Backstab costs nothing if you walk around the enemy, or a Bonus Action if you Jump, and provides essentially-permanent Advantage on Attack Rolls.
- High-Ground costs little to set up, or a bit more depending on the encounter, and then provides ongoing Advantage on Attack Rolls as well as giving the enemies Disadvantage on Attack Rolls against us.
- Foresight costs a level-9 spell slot, takes 1 minute (=10 rounds) to cast, lasts 1h, can affect only one target at a time, and gives ongoing Advantage on Attack Rolls (and ST and Ability Checks) as well as giving the enemies Disadvantage on Attack Rolls.
So basically High-Ground hands out the effect of a level-9 spell, without the long casting time, and to everyone. My understanding of its impact has just been reframed.
On a different note, is +2 really a "small" bonus ? Here I'm not interested in the source of the +2 bonus, just the magnitude. If Advantage is about a +3.33, a +2 is still about 60% of that bonus.
