Sorry you asumption is just absurd. Sorry... like completely absurd and has absolutely nothing to do with current game mechanics or those one can assume by using common sense.
Please have a look into your character sheet, if you even play a mage and aren't a coplete troll. Below your spellpower, there is another line showing you your regeneration. EVERY mage knows this regeneration. At the moment it is 15k / 5s regen for mages, improved by haste.
The mastery in Legion will clearly increase THIS regen. To asume we would bet 40% of max mana every 5 sec.... I facepalmed so hard.... Also your other plea to the devs.... I hope they will never implelemt this T18 bonus a s baseline and also won't listen to most of your pleas. It is just plain boring and a procc of a procc....
There a re a lot of things I'd like to see for arcane mages. Devs are on a good way..... PC gone *tumbs up* please also get rid of RoP....
LI2Atronach
Edit:
P.S: Legion mage will be like Cata Mage but without mastery and some utility talents.... if you remeber: Mage armor: 3%? of max mana every 5 sec and int increased max mana..... so just the same as the new mastery... more max mana and more regen....